There was a top secret pro hero event which was infiltrated by a villain, the villain possessed a reverse shape shifting quirk.

If hit by it the possessor of the quirk can temporarily change your species.

The villain was detained but not before your colleague (choose the pro) got hit by the quirk and was turned into an animal (you choose)

Tsukauchi in the force told the pros that the quirk wears off after 12 hours, but the animal may have instincts of a wild animal and should be guarded in case of being a danger to others.