Umi no Yami, Tsuki no Kage (OVA, 3 episodes, AniDB)

Requested before Jun 2019

* Based on a manga by http://anidb.net/cr10206 [Shinohara Chie], serialised in http://anidb.net/cr32438 [Shoujo Comic]. A http://anidb.net/ch85082 [girl]`s http://anidb.net/ch85083 [sister] becomes possessed by an evil force from the sea and tries to steal her http://anidb.net/ch85084 [boyfriend] from her.