Seiki Sakushu Mononoke Itan The Strange Tale of the Life Draining Specter

Synopsis

On his 20th birthday, loner Nagi Hiyori celebrates his birthday alone. In the evening, after finishing shopping, he is suddenly attacked by something strange! Unable to escape and about to die on his birthday, he is suddenly saved by a tenguu named Toushirou, who is tasked with protecting him. According to Toushirou, Nagi is the product of a half-youkai and a great youkai, and so his semen seems to have tremendous magical power. Thus, many youkai are now attracted to Nagi for it. Now, Nagi is caught up in the battle of youkai without even knowing it...?! (Source: Tokyo Mangasha, translated)