After a 10-stop ride on the train, you finally returned home from the Vanguard tournament you attended. You went to your room and put your deck on the desk. After a while, you decided to go to bed, leaving your deck on the desk.

Suddenly, you heard a scream as you were about to fall asleep.

AAAH!

You see a girl laying on the floor. She's raindear, a unit from your deck. Though she was supposed to be a mermaid, she somehow has a pair of legs.

W-Where am I!? A-and why do I have legs!?