Chapter Text
The late afternoon sun hung low over Musutafu like a lazy spotlight, painting the sidewalks in streaks of amber and rose.
Eri Sosaki sprinted down the familiar path from U.A. High, white hair now streaked with soft pastel highlights she’d begged Kyoka to help dye last month bouncing in its usual high ponytail she wore in school for comfort.
The single horn on her forehead, smaller and far less menacing than it had been in her childhood, caught the light like a polished pearl as at sixteen, she’d grown into her frame: Still petite, still carrying that wide-eyed cuteness that made strangers smile without knowing why but with a spring in her step that spoke of hard-won freedom.
Her school uniform skirt fluttered around her knees, backpack thumping against her back like a second heartbeat. Inside it rattled her notebook full of half-finished lyrics and a water bottle she kept forgetting to drink from.
She wasn’t just running to get somewhere, she was running toward something, toward the one hour (Or two, if she played her cards right) that made every grueling support-hero lecture at U.A. feel worth it. . .
Her music classes.
And more than that, her Kyo-nee.
The Heartbeat Agency building rose up ahead, sleek and modern with its signature soundwave murals etched into the glass façade, it wasn’t the flashiest hero agency in the city since Kyoka had made sure of that but it pulsed with quiet purpose: Rescue operations tuned to the rhythm of the streets, sidekicks who specialized in sonic support and crowd control and one very cool pro hero who always cleared her schedule the second Eri’s classes allow her to visit.
“Eri-chan! Looking sharp today!” One of the sidekicks called from the entrance checkpoint, a burly guy named Echo who gave her a lazy salute back when she snapped one off with exaggerated enthusiasm.
“Reporting for musical duty, sir!” Eri chirped, flashing him her brightest grin, the one that still made her cheeks ache a little from how unused to smiling she’d once been.
She’d come so far from the scared little girl who hid behind Mirio’s cape and thanks to her Grandpa, who’d finally handed over guardianship to Mandalay after years of gentle nudging, thanks to U.A., thanks to Aizawa, Deku, Mirio and thanks, most of all, to afternoons like this she was feeling every day less as the demonic child with a cursed Quirk and more like a normal, real person with hopes and dreams.
She waved at the rest of the crew, two more sidekicks sorting gear in the lobby and didn’t stop moving forward, sneakers squeaking on the polished floors as she beelined straight for the office at the end of the hall.
The door was already cracked open.
Kyoka Jirou sat at her desk, one earphone jack idly tapping a pen against a stack of reports, the other plugged into her phone playing something low and bass-heavy, purple hair fell in its signature asymmetric style, headphones resting around her neck like a crown but when Eri burst in Kyoka’s cool expression cracked into a genuine lopsided smile, the kind she only let slip when no one else was watching.
“Hey, Squirt.” Kyoka said, voice warm but trying to play it casual. She set the pen down and leaned back in her chair, arms crossing over her hero jacket. “You’re early. Thought you had that support-tech lecture until four-thirty?”
“I sweet-talked the professor into letting us out ten minutes ahead of schedule!” Eri announced, already dropping her backpack by the couch and launching herself across the room for a quick, fierce hug, Kyoka pretended to groan under the impact, but her free arm wrapped around Eri’s shoulders anyway, giving a gentle squeeze. “Kyo-nee, you smell like coffee and energy drinks again. Did you even sleep last night?”
Kyoka ruffled Eri’s hair, careful not to snag the horn. “Sleep is for people who don’t have paperwork from three different villain takedowns, but c’mon, let’s move to the practice room. You’re not getting out of warm-ups just because you’re cute.”
Eri’s heart did the fuzzy little flip it always did when Kyoka said stuff like that half big-sister stern, half secretly soft that show she care without trying to show she care.
Eri followed Kyoka down the short hallway to the soundproofed studio, the one lined with foam panels and posters of underground bands Kyoka swore were “the real deal”, instruments waited like old friends: Kyoka’s favorite bass propped against the amp, a microphone stand adjusted to Eri’s height, even a fancy piano in the corner she sometimes messed around with when her voice needed layering.
They settled in like always: Kyoka slung the bass strap over her shoulder, fingers finding the strings with effortless grace, Eri took her spot at the mic, rolling her shoulders and bouncing on her toes. “Okay, same as yesterday?” She asked, eyes sparkling. “Vocalization first? I’ve been practicing the breathing exercises you showed me, Mandalay says I sound like I’m about to summon a choir of birds or something.”
Kyoka chuckled, low and fond, plugging her jacks into the amp. “Birds, huh? Let’s hear it then Squirt, start with the scales nice and easy and I’ll follow your lead.”
The first notes rolled out of Eri like warm honey, her voice still carrying that ethereal clarity it had always had, even before she’d learned to love it. Kyoka’s bass joined in, deep and steady, a gentle anchor beneath the rising and falling scales. “Mi-mi-mi-maaa. . .” Eri sang, eyes half-closed, feeling the vibration in her chest match the thrum of the strings while Kyoka adjusted a knob, nodding along.
Eri still remembered how this all started; hearing Kyoka sing in the cultural festival, hearing that song Hero too, seeing all the 1-A class making a show that made everyone smile, especially herself after years of fear and tears . . . She wanted, no, she needed to be like that and her Kyo-nee was more than happy to help but it wasn’t just start singing; she learned vocalization, breathing and focusing like never before which was, for her, a challenge. . . But also make her progress feel more like a reward than anything.
“Not bad, kid. Keep your jaw loose—Yeah, just like that, you’re hitting those high notes cleaner than last week. Whatever Mandalay’s feeding you at home, keep it up.”
Eri beamed mid-note, cheeks flushing pink by the happiness of the praising. “It’s mostly just her trying to teach me how to cook without setting the kitchen on fire but I think the real secret is coming here every day! Kyo-nee, you’re the best teacher ever! Even if you pretend you’re too cool to admit it~” Teased a bit knowing that the mighty Earphone Jack was allergic to any compliment.
Kyoka smirked, but there was that faint flush, the one Eri had learned never to point out loud. “Flattery gets you an extra ten minutes, again and from the top.”
They lost themselves in it for a while. Eri’s voice danced over the bass lines, sometimes cracking into giggles when she tried to match a particularly funky riff Kyoka threw in just to mess with her.
It was easy.
Safe.
Happy.
The kind of happiness that still felt brand-new after all those years of fear and silence and Eri didn’t even notice the time slipping by until the studio door hissed open with a dramatic whoosh of air.
There he was.
Denki Kaminari, also known as Chargebolt by the general public and Denki-Nii by Eri, stood there in full hero costume with faint scorch marks from whatever chaos he’d waded through overnight, blonde hair stuck up in every direction, a few stray sparks flickering weakly at the tips like dying fireworks, dark circles sat under the eyes but that grin was as bright and dopey as ever. He leaned against the doorframe like it was the only thing keeping him upright, one hand dramatically clutching his chest.
“Twelve. . . Hours. . .” He groaned, voice cracking with exhaustion and theatrics in equal measure. “From three in the morning until. . . Whatever the heck time it is now, I zapped so many villains last night I think my brain’s numbing like in the old days, Jirou, your agency’s coffee machine better be stocked or I’m filing a formal complaint with the Hero Commission for animal abuse.”
Kyoka didn’t miss a beat, fingers kept strumming a lazy bass line, one eyebrow arched in that perfect mix of amusement and fake annoyance. “Look who finally dragged his sparkly ass in here instead of face-planting into his own bed like a normal person.” Her head shake a bit. “Rough night, Sparky? Or did you just miss my charming personality that much that you had to come straight up here and ruin my day too?”
Denki staggered forward a step, clutching the wall for support. “Charming? You? Ha! You’re mean, Jirou. Mean to your favorite neighbor hero even when I came straight here after shift change, didn’t even stop for a nap, because I knew you’d have sympathy! Or at least a couch I could crash and die for a bit and what do I find you doing? You’re already torturing poor Eri with scales! Save me, Eri-chan!” He turned those big, pleading golden eyes on her, dropping to one knee like a knight begging for mercy. “Protect me from Jirou being mean to me again! She’s gonna roast me alive if you don’t step in and save me my heroine!”
Eri burst out laughing, the sound bright and bubbly as it echoed off the soundproof walls, covered her mouth with both hands, but eyes crinkled at the corners. “Denki-nii, you’re so dramatic! Kyo-nee’s not even being that mean today. . . She only called you Sparky once!”
Kyoka snorted, setting the bass aside with a soft thunk. “Twice, technically. But who’s counting?” She stood up, stretching her arms overhead and shot Denki a sidelong glance that was equal parts teasing and. . . Something else, something softer around the edges that wasn’t nameable that easily. “Go home and sleep, idiot. You look like you got hit by a villain with a bulldozer Quirk. . . Again.” The fact that happened three times in six months show that bad guy really hated his guts.
Denki pushed himself up, still grinning and bumped his shoulder against hers as he passed in a very casual way, like it was nothing, but Eri caught the way Kyoka’s earphone jacks twitched just a fraction. “Nah, I’m good here, figured I’d swing by, see if my favorite sound hero needed backup on her next patrol run later or whatever. Plus, Eri’s here and that automatically wins the “Best part of my day” in all honesty.” He ruffled Eri’s hair too, just like Kyoka had, but gentler, like he was afraid of breaking her although eyes lingered on Kyoka for a second longer than necessary, that dopey smile softening into something warmer, almost fond.
Kyoka rolled her eyes, but Eri didn’t miss the faint blush dusting her cheeks, the one she tried to hide by turning toward the amp and fiddling with knobs that didn’t need fiddling.
Eri laughed again on the outside, but inside her brain was already whirring like one of the support-tech gadgets she built in class.
Why did he come here?
That was the question. . .
He’d just pulled a twelve-hour graveyard shift from 3 a.m. until now, whatever “now” was.
Most people would crash in their own agency.
Go home.
Shower.
Sleep for twelve more hours.
But Denki? His first stop was right next door, at Kyoka’s agency, still in full costume, still roughed up to complain, to banter, to stand a little too close and call her “Jirou” in that voice that wasn’t quite as silly as it used to be back in high school.
She squinted, just a tiny bit, watching them from her spot by the mic.
The way they walked around each other now, just like magnets pretending they weren’t drawn together.
Denki would step in to grab a spare cable off the table and Kyoka would shift just enough that their arms brushed once more. . . The way they looked at each other was electric: Kyoka’s smirk sharp on the surface but her eyes going all liquid when Denki called her mean Jirou and Denki, always the class clown, trying so hard to act cool, shoulders back, smiles popping like he was totally fine and normal. . . Until Kyoka teased him and his whole face went soft; Like the sun coming out after a storm.
Eri tilted her head, ponytail swaying.
“I’m not dumb nor blind not to see the obvious implications here. . .” She thought, the realization settling warm and mischievous in her chest. . .
Those two are in love.
She didn’t say it out loud, not yet at least, but as Kyoka muttered something about “charging stations for dumb electric heroes” and Denki fired back with a laugh that filled the whole room, Eri felt her lips curve into a secret little smile.
Kyo-nee deserved this.
Denki-nii too.
And if Eri had to play the world’s cutest, sneakiest matchmaker to make sure they stopped pretending otherwise?
Well. . . She was happy to support two of her favorite heroes.
After all, she wasn’t just here for the music anymore.
Denki’s eyes lit up like twin live wires the second they landed on the spare guitar propped in the corner of the studio, a sleek black electric one with bright yellow lightning-bolt decals streaking down the body like captured thunder.
“Oh man, perfect timing!” He said, already shuffling over despite the way his shoulders sagged from the long shift. He grabbed it like it was an old friend, slinging the strap over his neck with practiced ease. “Mind if I plug in? I’ve got twelve hours of villain zapping still buzzing under my skin so I gotta work it out before I face-plant.”
Kyoka didn’t even glance up from adjusting her bass amp, but her smirk tugged at one corner of her mouth. “As long as you don’t fry my cables again, Sparky. Last time I had to call in a tech just to get the feedback to stop humming ‘Chargebolt’s Greatest Hits’.”
Eri watched the whole exchange with wide, innocent eyes, her ponytail swaying as she tilted her head and she couldn’t resist poking the obvious. “Kyo-nee, since when do you keep a lightning-themed guitar lying around? It’s so. . . Flashy.” And by flashy she meant it look totally Denki. “Looks like it was custom-made for someone who shoots electricity out of his fingers on a bad day.”
Kyoka’s fingers stilled on the strings for half a second and shot Denki a quick sideways glance, the kind that tried to stay cool but landed somewhere softer. “It’s not mine.” She said, jerking her thumb toward him. “It’s his. Idiot always leaves it here after we jam together, you know. . . Music sessions until night falls and we lose track of time so it’s easier to let it here than him hauling it back and forth every day.”
“Super convenient!” Denki agreed cheerfully, plugging in and strumming a quick, flashy power chord that sent harmless blue sparks dancing along the fretboard. He winked at Kyoka, who rolled her eyes but couldn’t quite hide the faint blush creeping up once more. “Best acoustics in Musutafu, plus Jirou’s got the good snacks stashed in the mini-fridge, it’s a win-win for me!”
Eri blinked slowly, her smile frozen in place like a perfect little angel. Until night? They jam together until night? And he just leaves his guitar here like it’s his second home? Like it’s totally normal for two “professional” heroes to hang out alone in a soundproof room for hours after dark? Her brain screamed internally, the words clawing at her throat.
ARE YOU FUCKING SERIOUS?!
Hanging around Bakugou was clearly rubbing off on her vocabulary in the worst (or best?) ways. She had to bite the inside of her cheek hard enough to taste copper just to keep her face sweet and unsuspecting.
Out loud, she only let out a bubbly little laugh. “Ohhh, that makes total sense! You two must make the coolest music together. Like, electric and bass; total powerhouse combo!”
And just like that, they dove in.
Denki’s guitar wove bright, energetic riffs around Kyoka’s deep, steady bass lines, the two instruments locking together like they’d done this a thousand times, Eri stepped back up to the mic, her voice rising clear and confident through the warm-ups, then into the half-finished original she’d been tweaking all week.
The notes filled the studio like sunlight through storm clouds; Eri’s ethereal tone floating high while Denki added playful licks that made her giggle mid-phrase and Kyoka threw in teasing counter-melodies that somehow always pulled everything back into perfect harmony.
They bantered the whole time, childish and effortless and laced with something that made Eri’s little-shit matchmaking radar ping like crazy.
“You’re rushing the bridge again, idiot.” Kyoka muttered, but her foot was tapping along to his rhythm.
“Yeah, well, your bass is too distracting.” Denki shot back, leaning in just enough that their shoulders brushed. “It’s all sexy and steady and—Ow, hey! Did you just ear-jack me?”
“Focus, Sparky.”
Eri watched them from behind the mic, cheeks aching from how hard she was smiling on the outside while her brain spun cartwheels. The way Denki’s eyes went soft every time Kyoka called him an idiot. The way Kyoka’s smirk faltered into something almost shy when he nailed a riff or called her “rockstar” it was so obvious, so painfully, adorably obvious and they were both acting like it was just another day in their lives was excruciating.
A few hours slipped by in a haze of laughter and chords and the occasional spark that Denki swore was “totally under control”. The sky outside the small studio window had turned deep indigo by the time a familiar, sunny voice echoed from the hallway.
“Eri-chan? You still in there?” Mirio Togata poked his head through the door, his bright smile lighting up the room even brighter than Denki’s guitar. He was in civilian clothes; simple jacket and jeans but carried that same unbreakable warmth he’d had since the day he’d first reached out a hand to her all those years ago.
“Mirio-nii!” Eri exclaimed, setting the mic down gently and rushing over for one of his careful-but-still-enthusiastic hugs. She waved quick goodbyes to Kyoka and Denki, who were still lingering near each other by the amps like they had nowhere better to be. “Thanks for the session, Kyo-nee! Denki-nii, your guitar solo was awesome! See you tomorrow?”
Kyoka ruffled her hair. “Wouldn’t miss it, Squirt. Get home safe.”
Denki flashed her a thumbs-up. “Night, Eri-chan! Tell Mandalay I said hi and that her stew is still the best in Japan.”
In the car on the way back to the house Mandalay had turned into their cozy home, Eri chattered nonstop, the words tumbling out like lyrics she couldn’t hold back.
“U.A. was good today. Professor Power Loader let me tweak the new support gauntlet prototype, and it actually didn’t explode this time! And the music session was the best part of my day, Kyo-nee’s bass lines are getting even tighter and Denki-nii showed up after his long shift and we just. . . Jammed. It was so much fun! I think I finally nailed that high note on the bridge I’ve been struggling with.”
Mirio listened with pure delight, one hand steady on the wheel while the other occasionally gestured along with her stories. His laughter filled the car, warm and genuine like always.
“That sounds wonderful, Eri! I’m so proud of how far you’ve come. You’re blooming like one of those flowers we used to talk about with your strong roots, bright petals. Music really does suit you and it’s great that Jirou and Kaminari are looking out for you like that. They’ve always been good at lifting people up, I remember when I met them in that battle exercise, he was always trying to protect her and she kept yelling him he was getting in the way. . . I actually tie them up together, it was hilarious!”
Eri smiled, staring out the window at the passing streetlights for a moment.
Then, in her sweetest, most innocent voice, the one she’d perfected for getting extra dessert from Mandalay, she tilted her head.
“Mirio-nii. . . You know a lot about a lot of things, right? Heroes, fighting, being brave. . . But do you know anything about romance? Like, when two people are obviously into each other but they keep acting like they’re just really good friends who ‘jam together until night’ and leave their stuff at each other’s places and blush but pretend they don’t?”
The car didn’t swerve just because Mirio was too much of a pro for that but his hands tightened visibly on the steering wheel, sunny expression flickered through surprise, confusion and then full protective-father-figure panic in the span of two seconds flat. His cheeks went pink, eyes wide as dinner plates.
“R-romance?! Eri-chan, sweetheart, is there. . . Is there someone at school? A boy? Or—or a girl? Whoever it is, you can tell me! I need to meet them immediately! We should talk about boundaries and respect and, oh no, are they treating you right? You’re still so young and I know you’ve grown so much, but if anyone’s making you feel even a little unsure we can call Mandalay right now, or Tamaki, or even Midoriya! He’s great with advice, well he is actually terrible about romance, but—I’ll make sure they know exactly how special you are and that they better be perfect or else I’ll just. . . I’ll just phase right through their defenses and have a very polite conversation about—”
Eri blinked, realizing too late how her question had landed.
Inside, she was both giggling helplessly and facepalming so hard it echoed. Oh no. He thinks it’s about me. But outwardly, she kept her voice light and reassuring, patting his arm gently. “Mirio-nii, it’s not about me! I’m just. . . Curious, for a friend, a very obvious friend who doesn’t see what’s right in front of her.”
Mirio let out a huge breath, shoulders sagging in relief, but the protective glint didn’t fully leave his eyes. “Oh. . . Oh! Well, in that case. . . I mean, I’m no expert, but love’s kind of like being a hero, right? You leap in, you trust your gut and sometimes you end up flat on your face but it’s worth it if the person’s right there catching you.” He glanced over with a sheepish grin. “Why? This ‘friend’ of yours, do they need some big-bro advice?”
Eri just smiled her secret little smile, the one that said she was already three steps ahead in the matchmaking game. “Maybe. But I think they’re doing okay on their own. . . For now.”
But that won’t stop super-agent of love Eri to step in and crack the case.