Shinobi Stones are small pendant-like objects that can be equipped to boost ones abilities. They appear in Senran Kagura 2: Deep Crimson.
In Senran Kagura 2: Deep Crimson, Shinobi Stones can be equipped via the equip menu. They are unlocked by playing through Special Mission. The player can equip up to 3 Shinobi Stones at a time.