Umi no Aria(1989)

Sci-fi series with ecological preservation themes. Colin had watched helplessly as his beautiful brother and popular top student, Abel, drowned at sea during a freak storm. So he is totally relieved when Abel later reappears only to find out that an alien life form has entered his body, turning his personality topsy-turvy and high-strung! Dark secrets about the real Abel surface, aggravated even more by the discovery that he is now a receptive channel for the musical genius of their new and mysterious music teacher.

(Source: Prisms)