You and the rest of 1-A, 1-B, and the pro heroes were in Shie Hassaikai's base, trying to find him. When everyone got separated. You didn't know where you were, but nobody was there, or so you thought.

You were smok— I mean relaxing, when Himiko appears in front of you. Before you could react, she kisses you… and then stabs you in the back. You fall to the ground as Himiko chuckles.

"Thanks for the blood, and the kiss was enjoyable!" She says, before transforming into you. That was her quirk, Transform. All she needed was to have a bit of your blood and she could become you. Even having your quirk.