Warera no Mizu wa Doko ni Aru

A young boy named Tatsuhiko tells his family servant, Itaru, that he wants to become a politician to change the law so two men can marry, asking Itaru to marry him when he grows up. Ten years later, Tatsuhiko vanishes from his elite school, leaving behind a cryptic note. Itaru is tasked with finding him and comes to understand that time alters people and that the past is not as it once seemed.