Young warrior, Onimaru is given the Oni Gauntlet as he rushes to defend his village from the demon hordes of Nobunaga Oda. Onimaru soon discovers from the old man Sandayu, that although he has been living in the peaceful province of Iga, he is of the Oni clan and had been secreted away. Additionally, with the power of the Oni Gauntlet, he can absorb the souls of enemies and use the demon Genma stones to recreate lost weapons and armor. With this new knowledge of who his is and of his destiny, he assembles a hasty squad of fighters including his sister Ororo and sets off to avenge his province and stop Nobunaga's demonic war upon the land.

Onimusha Tactics is a turn-based strategy game between the player's side and the enemy's side. In each level you can bring a squad of no more than 10 people. There are no items to buy or sell, however equipment is available and customizable. Upgrades of existing weapons and armor can be done using the defeated souls of enemies absorbed into the Oni Gauntlet. New weapons and armor can be found or created through fusion of Genma Stones. Recipes must be found for each separate item before it can be fused.

Most characters have a normal attack, the ability to use items and several special techniques for battle. Additionally there is an issen ability that randomly shows up and allows your character to counter-attack and instantly kill any enemy who foolishly attacks that character directly in the next round.