Otaku! is a role-playing game, set in a small remote city of Japan, where the story focuses on how a high school student named Kuwan Otaku, who has the gift to see mysterious entities of light, obtains a power and decides to use it to investigate obscure events surrounding the disappearance of missing students.

The game features a mixture of elements, from Visual Novel to various Rpgs. During battle sequences, the game uses Side Linear Motion Battle System. Damage dealt to the opponent fills a "Tag-Gauge". When this is full, an "X Attack" can be triggered, allowing the player to perform overdrives.