Highschool of the Dead: Drifters of the Dead
An OVA of Highschool of the Dead bundled with the 7th manga volume.
Komuro and the gang stumble upon a deserted tropical island that looks to be free of zombies. They make use of this wonderful opportunity and dress up in skimpy swimsuits and have lots and lots of fanservice fun.
Hallucinogenic substances are involved.