Unfortunately, anon, I haven’t watched/read BNHA but I think I have enough of an understanding to fill this prompt (whether as a ficlet or a brainstorm) so I’ll try my best not to to mess it up too badly.
Tetsuki is no stranger to the hero/vigilante lifestyle–and I’m not just talking about Deuteranomaly. She is originally (yes, even before Trailblazers) a secondary character from my original series Counterclockwise.
Counterclockwise does mainly follow Leanne Peridot’s not-so-kind travels through time, but “before” that happens she was the fifth member of a team of teenaged vigilantes, one of whom is Tetsuki Kaiza, aka Thunderbolt (who I then co-opted for my crazy continuous reincarnations through fandoms series, the poor dear).
Given what I understand of the world of BNHA and what I’ve written in the world Counterclockwise… they’re not ENTIRELY incompatible. Or, rather, if Tetsuki were in the BNHA world, she would have a fairly similar background as in Counterclockwise.
Because the thing is, even without Counterclockwise, I would want Tetsuki to be an older, near burnt out pro hero who has been told to take some time off and recuperate from the godawful mission that caused half of her team to die/go missing. And, of course, they’re hoping she’ll find an apprentice/sidekick to pass along her techniques but mostly they just don’t want to her burn out completely or, worse, go evil.
Obviously, they want her to take on Denki Kaminari as her temporary student, given his Electrification quirk, and maybe she does help train him or give him some tips (honestly, he needs to learn how to increase his capacity, that one hour short circuit bullshit is going to get him killed) but the thing is:
Thunderbolt’s quirk has nothing to do with electricity.
Probably in the BNHA world Tetsuki’s parents have pretty mild/less showy quirks–one of them has psychometry and the other has augmentation/negation or something like that–so it’s very surprising that her quirk is so powerful and multifunctional (yes, she is known for the electricity, but she’s also been seen doing things like casting illusions or forming barriers and such… though most believe that’s her using electricity at such an high level of intricacy that it manipulates light waves or neurons or the electromagnetic charge between atoms?)
Turns out her quirk is simply Remembering.
Given this would be a Viridescent ficlet were I to write it (and I am leaning towards doing so because this is a pretty cool idea, though I should probably learn more about BNHA before attempting it)… I am leaning towards this being one of her lives where she doesn’t remember everything immediately.
More like Externality in that sense (where she remember things gradually or unlocks memories as she needs them in times of stress). Instead of as in Multiphenomenal and that Power Rangers!Viridescent where she just knows pretty much right away, or the opposite with Iron Will and Deuteranomaly where she never really remembers but only has Very Strong Feelings/Hunches about certain things.
Which would give her story in BNHA an interesting progression because it’s assumed, that she’s at the top of her game–ridiculously powerful, an alumni (if UA isn’t a new thing, I’m not sure) who is giving out pointers to the next generation–and it turns out hey, she’s only used her “real quirk” to Remember her previous lives’ abilities but none of the life lessons or friendships or the fact that she’s destined to die before age 25.
And guess how old she is now.
I mean, the main part of it will be her recovering from losing half her team (and Remembering all the other people she’s been close to) and realizing that being close to people isn’t entirely a curse. So her lessons to Denki become less reluctant and she starts to give out pointers to the other students (and hopefully mitigates some of the frustratingly persistent sexism that is shounen series’ handling of female characters ie LET THEM FIGHT) and she becomes kind of like a TA at the school.
And then, like in Counterpoise canon, she goes supernova to protect everyone.
Or maybe, in line with this post about the lessons BNHA teaches, she doesn’t go supernova to protect everyone. Maybe she considers that but is instead convinced to maintain a barrier around the school–which ought to be easier except so much power is needed. And she doesn’t tell anyone, but it’s too much power–it’s draining her too much–and when the crisis is over, it turns out that even though she was able to maintain it her body couldn’t handle it. And so she still ends up dying, but not in a huge flashy way that glorifies self-harm.