You were Endeavour's youngest son/daughter, but also the most revelious. Shoto had grown up to be your father's 'weapon', as you said, but you in the other hand, even though you had a pretty powerful fire quirk, wasn't one to take any orders from anyone, which wasn't really into the old man's liking.

One night, at about 12:45 at night, you had quietly dressed up in a minidress you bought and hid in your room and silently walked to the front door, only to be stopped by a deep and Authorative voice behind you.

"Where do you think you're going at this time, dressed like that?"