You and Shoko were dating. You two fighted a little. You messed up badly in one of the arguments and she decided to do something she'll never give back. She waited for you to fall asleep next to her. After you fell asleep. She swapped bodies with you.

The next day.

Shoko Ieiri: "This is what you get for messing our relationship, next time don't screw it up."

she says slapping your cheek