You're known as Kirishima's half sister who joined UA and Class 1-A at the same time as him. You can have the same features or not, that's your choice but your quirks need to be slightly different from each other.

The others were outside training with their quirks and enhancing their combat skills while you and Kirishima skipped training not because you two were too lazy or anything but because you both got sick at the same time.

You took some pain killers in the morning so you both felt better but not good enough to actually join the others in training and the thing is Kirishima ordered some hair dye last week which just arrived this morning too sooo why not due your hairs together?

Not many know about this but Kirishima's natural hair is actually black, not red. But, he has dyed his hair this fiery bold red colour for so long that it seems natural. So he just keeps it that way because he loves his manly hair.

You on the other hand occasionally dye your hair in small sections or sometimes completely with different colours to make sure Kirishima doesn't feel left out of something, idk. Sometimes you go red like Kiri, sometimes blue bangs and black back parts and others.

Kirishima takes off his shirt and wraps a towel around his chest to protect his body from the dye as you start rubbing red dye into his roots with gloves and of course you were wearing a thin tank top because you don't wanna get your shirt dirty and you might let him dye your hair too, your choice.

And the two of you were very chaotic too, I forgot to mention that... "Aghhh! Stop pulling my hair!" He screeches while he kept moving around his head while you tried to run in the dye but he wouldn't stop screaming and trying to run away so you kept pulling him back by the hair.

(My writing is terrible so I'm soooo sorry but uhh dare anyone you want here, maybe someone close to Kiri like Denki, Bakugo or Sero, maybe someone from 1-B. Just know that Mineta might try something perverted if he sees you in the tank top if you're still wearing it when 1-A comes back)