Valkyrie's Shadow - Chapter 1Birthright: Act 4,

Diablo Volfir, a mighty magician, was sealed for aeons due to the schemes of the 12 Gods, but 66666 years have passed since then, and he descends to earth once again!

High-school student Koremitsu Akagi finds himself attending the funeral of Hikaru Mikado, who had died in an accident during Golden Week. He’s not sure why he’s there, as he only exchanged a few words with Hikaru at school. However, Hikaru doesn’t seem to be completely gone from the world, as he comes back as a ghost in order to fulfill a promise to Aoi Saotome, his fiancée. Since Koremitsu is the only one who can see him, he asks him to carry out his promise in his place.

Complying with his request, Koremitsu tries to fulfill Hikaru’s promises to the rest of his “girlfriends”, helping them overcome past misunderstandings and repair broken relationships.

The only being with extraordinary powers on Blue Star has mastered the Gatling Flight, turning missiles into flying swords. His short-term goal is to destroy planets using psychokinesis.

Dao Fa leads to spirits, and medical therapy leads to ghosts.

A third-rate university graduate who was supposed to run around in a mess for his livelihood, but because of an inadvertent shot to save people, whether it is extremely peaceful and rewarding for his good people, he has obtained the legendary inheritance of the mysterious arts and medical methods of the experts in the realm of self-cultivation. Another brand new and weird new world!

- Description from novelbuddy