Kanetsugu Ookura
About
Kanetsugu taught Aiko how to use spiritual powers. He sexually abused both Hikiko and Aiko, murdering both once he deemd them "nuisances", and setting fire to the Mejiro Villa to cover it up. Aiko's body is buried in his backyard, with a tree planted over it.
After Aiko merges with Yuko, Yuko remembers that she had been prepared to be a vessel for Aiko's spirit, which involved Kanetsugu abusing her in the same manner he did with Aiko.