There two types spirit artes he knows. The first is summoning. In which the user calls upon multiple other spirits to aid him in combat. Or spirit fusion where he fuses with and combines with a stronger spirit.
With this there are smaller spirit artes such as spirit enchantment to allow a high rank spirit to possess your weapons. Ex: Is his blade Emperion- imbued with a high rank fire-solar spirit that can take a physical form. Each enchantment has different effect for him he can switch elemental forms giving him resistance to those elements he takes. Each form has it's own natural weakness. For ex:Water->ice->fire->water->earth, Fire- > Light-><-dark->divine light->abyssal black->Ying-yang