One day, Ezawa Jun, who has trouble with work and in love, gets a ryukin from a goldfish scooping game at a festival. However, she is actually a beautiful girl and she suddenly turns into a human form and appears in front of Jun. Called Ryu, she is looking for the legendary black ranchu and asks Jun for his help. The two strangers begin living together and growing closer. Their fate goes in an unexpected direction.

"I found you. It was destiny."