The Strongest Vampire in the World

It is an anti-onmyoji novel. The protagonist will never use the onmyoji of the island country, and will kill the onmyoji with supernatural powers. There are vampires, onmyojis, and various heroines from Gensokyo that are loved by anime fans. In order to defeat the Onmyoji, the protagonist has to frequently exchange powers with the beautiful girl who lives in his body. The price is that each time you gain a power, you will lose one year of memory. There is a payoff and a reward. This book is of the humorous type.