Possessioner is primarily a Japanese-style adventure game. The player selects verb commands from a menu and combines them with objects appearing afterwards to interact with the environment and trigger events. Navigation is menu-based as well. The game also contains sporadic turn-based battles against the Possessioners and their minions. Four female combatants have a variety of attacks at their disposal, but the battles are fairly simple and there is no role-playing system. The game contains scenes with nudity and explicit, exclusively lesbian sex scenes.

The year is 2035. A series of mysterious incidents began to occur in Tokyo. Young women disappeared under strange circumstances, and returned brainwashed, commanding armies of bionic monsters and assaulting human settlements. Such women were called "Possessioners". A special all-female squad was formed to face them in combat and bring them back to humanity.