While games the world over are going crazy for petting dogs, Nioh 2 lets you stroke a cat. Not a real cat, a strange cat ball Yokai. As you explore the game you will come across these small creatures, called Scampuss, and you can interact with them to let them know you are good friends.
When you interact with a Scampuss, you are inviting it to tag along with you on your adventure. The Scampuss will roll along behind you, ready to help out in any way it can, even if those ways are limited.
The first thing a Scampuss does for you is to increase your Anima. The Scampuss will bestow a buff on you that allows you to passively generate more Anima. This will allow you to use more Soul Core moves, and Bursts Counters.
While following you, the Scampuss will also try to help you out in fights. It can only bounce at enemies, doing small amounts of damage, but it will become more effective when you enter the Dark Realm. As a Yokai, it will become more powerful there, changing from a cute little creature into a spikey ball of fur, and doing more damage to enemies.
Scampuss are not rare and will pop up once or twice in most levels in the game, so keep an eye out for these little round ghosts, and take advantage of their willingness to help you.