Someone posted a thread about hidden instances in the game. This is a description on the Kappa and their love of human colons. In Nioh 2, when they grapple you, they appear
The Art of Eoghan Kerrigan - Playing Nioh made me want to draw some kappa. | Facebook
Japanese Yokai Monster Kappa 河童 Linocut Lino Print Hand - Etsy Finland