A small, lone Kappa miraculously survives over 200 years into modern day Japan, when he is found by young Koichi. Coo, who is secretly adopted by Koichi's family, searches with his new human friend for unpopulated places in hopes of finding any remaining of his kind.
- Genre: Animation, Comedy, Romance
- Studio: Dentsu Tec, Mitsui Bussan, SKY Perfect Well Think, Sony Music Entertainment, Summer Days With Coo Committee, TV Asahi, Shochiku, dentsu, Shin-Ei Animation
- Keyword: river, swimming, adult animation, sumo, back in time, corrupt official, kappa
- Cast: Kazato Tomizawa, Takahiro Yokokawa, Naoki Tanaka, Tamaki Matsumoto, Ken'ichi Nagira, Nanako Hirata