Her Quirk manifested at the age of four, only becoming apparent when a friend tried to show her something on the TV only for the said TV to quit working when she touched it. Of course, her accidentally shocking everyone who so much as grazed her afterwards didn't help either, leading to one very confused and unsettled Masumi Sera getting shoved out the door with a wooden broom when Shuukichi finally came to get her.
After that it was a whirlwind of apologies for the broken TV and tests just to figure out the obvious: Masumi had inherited her father's Electric Charge Quirk, much like Shuukichi himself had. The good news from this was now she could learn to use it properly instead of randomly draining every electric device she came across. The bad news however, was that only Shuukichi could really do anything when Masumi had built up too much charge, and until she got things under control people were generally a bit wary of letting her hang around too long.
Of course, opinions changed once she did get it under control. Suddenly Masumi went from being a danger to electronics and people to someone who could be a great hero one day, someone with a rare Quirk who could potentially put it to use, unlike her shogi focused brother. And no one would let go of that fact, all through elementary and middle school. No one would let it go, leaving her incredibly worried about what might happen if she failed, if she failed to meet all those expectations. And her learning Jeet Kune Do from her distant eldest brother didn't help much either, as that just sent the message that she was versatile, could handle anything if she became a hero.
And so in spite of her mother's initial plans to move to Britain, Masumi decided to not just apparently run away and instead applied for UA High at the very first opportunity. She wasn't going to run away, wasn't going to become a failure, was determined to live up to the expectations placed on her by pretty much everyone around her. (Then again, this came as no surprise to anyone who knew what she was like. Masumi had become quite protective of those around her over the years, so maybe it was for the best that she was trying to attend the best school for heroics around, so that she'd be better prepared in the future.)
Eventually the day of the entrance exam came, and Masumi went in trying her best to look like she was completely confident in her own skills. She was going to do this, and she was going to succeed no matter what. She was not a failure.
Note: This won't be Masumi-centric, I will give focus to other characters.
Quirks in this chapter:
Electric Charge: User can store electricity from surroundings and then discharge it later at will. Stored electricity must be discharged directly into some sort of object at some point and cannot be discharged into the air. Too much stored electricity can cause the user to involuntarily discharge into anyone or anything that they make contact with, and in extreme cases even muscle spasms in the user.
Known users: Tsutomu Akai (deceased), Shuukichi Haneda, Masumi Sera