From PlayStation Universe: “Onimusha: Warlords has plenty of collectibles and secrets to find. Released originally on the PlayStation 2 this remastered is packed with collectibles to find, hidden weapons to acquire, and secret game modes to unlock. Oni-Spirits is a mini-game that sees Samanosuke breaking pots to free souls. He must break a certain amount before his health runs out. The catch is that enemies appear in each of the twelve stages that destroy the pots.”
Source: N4G PC Onimusha: Warlords Oni-Spirits Mini-Game How To Unlock the Oni-Spirits Mini-game