Kanshu entered the temple on Mt. Hiei and became a Chigo (child in Buddhist possession) at the age of 11, afterwards becoming a priest and receiving the kanjo (initiation of a succession where water is poured onto the successor's head) from Yokei in 985.
11歳の時比叡山に上って稚児となり、その後出家して、寛和元年（985年）に余慶から灌頂を受けた。