"big sister", but also a colloquialism for a young adult woman) and chanbara (チャンバラ, "sword fighting").

The series centers around Aya, a cowgirl who wears a scarf and wields a katana, who is pitted against hordes of zombies and other monsters.

Players guide their characters through the stages, completing tasks while fighting through enemies.

The player-character's weapon becomes progressively covered in blood, causing their attacks to be slower and to inflict less damage, even getting stuck in enemies if it gets too bad.

To recover from a blood frenzy, the player must use statue items, which are dropped by dead enemies.