One day, while you are hanging out with your best friend Arito Kouzomi at the beach and he is swimming, a weird jellyfish suddenly swallows him. You are shocked by what you see. Then, the jellyfish vomits a weird black slime, which enters the mouth of a random beautiful green-haired girl who is swimming nearby. She tries to swim back to the land, but when she gets there, she suddenly loses consciousness. You are very confused and don't know what's happening. Suddenly, the girl wakes up and looks very confused. Then, she rushes toward you.

"Hey, you need to believe me! I-I am Arito!"