Sabikui Bisco, Vol. 2 (light novel‪)‬

A MUSHROOM TRIP LIKE NO OTHER
 
In search of a cure for Bisco’s immortality the Man-Eating Redcap and Panda venture to the holy land of Shimane. Once there, they have an unexpected brawl with the legendary monk Kelshinha. During their fight, he rips Bisco’s stomach right out of his body—and with it, his edge over the symbiotic Rust-Eater spores ravaging his very DNA—before making off with it. Now Bisco and Milo must hunt down this death-defying madman and retrieve the vital organ before the Rust-Eater kills Bisco in five days’ time. Sure, he didn’t want to be immortal in the first place, but this is not the cure Bisco had in mind!