The central idea is easy to state and easy to get wrong. A kamuy is not a spirit inside a bear. In the Ainu account the kamuy live in their own land, where they have houses and families and look much as people do, and when one of them comes to the human world it puts on a body, the body of a bear or an owl or a fish, and brings its meat and fur with it as a gift. The animal a hunter meets is the visitor and the costume together. What the hunter owes is what a host owes a guest who has arrived bearing presents: courtesy, food, drink, and a proper send-off home.
This turns the whole relationship around from what an outsider expects. Ainu practice is less about petitioning powers than about discharging obligations of hospitality, and the exchange runs both ways. A kamuy treated well speaks well of the household on its return and comes again. A kamuy treated badly does not, and the failure is understood as a breach of manners with consequences.
The category is wide. Fire is a kamuy, and the hearth goddess is the one every household deals with daily and the intermediary through whom messages go to the rest. Mountains, rivers, illnesses and even well-made tools can be kamuy. What is not a kamuy is aynu, the human being, and the two words define one another.
The instrument of the relationship is the inaw, a stick of willow shaved so that the curls remain attached, set up at the hearth, at the eastern window, at the sacred place outside the house and wherever a kamuy is addressed. It is offering, message and marker at once.