Rui Kamishiro was an ordinary merman who lived on his bottom with his family. Over time, he met a seemingly kind guy from the land and they got along well, or so Rui thought. It turned out that Tsukasa was a scientist and tricked Rui into sleeping and now keeps him in his laboratory in a very narrow semblance of a pool. He studies Rui and sometimes tests/conducts experiments, having completely lost the trust of the frightened merman. Rui has a collar-like thing around his neck.