Mizu no Yakata水の館 ; Mansion of Water ; mansion de agua (spanish)

This is the one shot of the movie that Sana and Naozumi starred in from Kodomo no Omocha. A 14 year old boy, after the loss of his parents, starts researching his older brother, who has mysteriously disappeared several years before. He finds him in a strange palace, with his two friends who had also disappeared. At first, the boy is happy, but then he discovers that something horrible has happened in that palace, and he might just become a victim too.