High school can be a complicated time for young men, especially for those named Ichirou Tachibana. Ichirou knows his homeroom teacher Yuuko Morino's biggest secret: she is a witch! When fellow classmate and witch Lily Ramses Futaba catches him peeking on Yuuko, she decides it is the perfect time to use a new spell she has acquired and turn Ichirou into her familiar servant. Lily's planned antagonism toward Ichirou goes awry when the spell turns him into some sort of twisted, purple, tentacle monster. Now he must directly acquire sexual energy from witches in order to sate the tentacle monster's lust and retain elements of his humanity. To make matters worse for the two witches, Ichirou's new form gives him the power to control them to satisfy his basest desires! The trio also finds out that the spell Lily acquired was sold to her deceptively and intentionally made to appear genuine. Amidst all the sexual misadventures in Witches and Tentacle, they are about to discover that something far more sinister is at work, and they are but pawns within a larger game.