It's wish fulfillment. Sometimes it grows boring the more you read. He becomes op to quickly. In less than 100 chpater he become pinnacle powerhouse. After he travel to other worlds, he just swipe them all (Well, dxd(+champione/god slayer) world combat power far more than other world so far (akame ga kill, code geass)

Interesting...

This is leisure slice of life fanfic i think, there is no complicated drama, battle, etc. The problem resolve easily. In first chapter, he reveal world travel ability to jouichiro, nakiri family, gin, in to another chapter, to others like elite ten and tootsuki graduates. There is no conflict or complex plot or scheme. It's very leisure and easy mode

Already read this in another mtl sites, but this has better translation