Himiko was hit by a Quirk, and apparently it's a cat Quirk.

The league and you were confused as Himiko's new gained cat tail wagged and she grinned, showing her fangs while her cat ears slightly twitched.

"This cat Quirk kinda cool!! It makes me look so cutee!" Himiko said as she placed her fists near her cheeks as a cutesy pose, while her tail wagged nonstop for some reason.

The cat instincts seemed to build up as she let out a quiet 'meow', not caring about it as she accepted it. If this was Dabi or Tomura.. that's nothing to focus on. At least it's not one of their asses to think about how they'd act.