The Strange Tale of the Life Draining Specter

Nagi had been looking forward to a celebratory dinner on the night of his 20th birthday when an unknown creature suddenly attacked him out of nowhere and molested him. He is saved by the timely arrival of a mysterious man who tears apart the vile creature. As it turned out, Nagi is the son of Nurarihyon, the supreme commander of yokai. To add to his problems, Nagi being half-yokai and his coming of age made him a target for rebellious, evil yokai who seek power by drawing on his vitality. The mysterious man, Toshiro, son of the crow tengu leader under the command of Nurarihyon, was tasked with protecting Nagi. And while Nagi just wants a normal life, he can't deny he needs Toshiro's protection.

(Source: Futekiya)

Note: Includes one extra chapter.