Disciple of a Demonic Cult 

Time travelling from the majestic era after the Recuperation of Reiki, he became Kimura Kazuki, a 16-year-old high school student in Japan, one year before the Reiki Recuperation.

Tentatively, he set out to hone himself to the bone, burning candles at both ends to stockpile resources in preparation for the imminent Recuperation of Reiki. His goal was to be many steps ahead of all humanity when the time comes.

However, it seemed like fate had decided to play a cruel trick on him.

One year later, the Recuperation of Reiki... did not happen as expected.

The Sword Deity in Tokyo

And Spiritual Academy too, Kimura Kazuki thought to himself.

It was important to note that one's memories were engraved in the depths of one's soul, while the brain only functioned as storage space. The answer as to why someone who suffered a concussion and amnesia could retrieve their memories back was because they had not damaged their soul during the event.

It was also the reason why people who died and turned into spirits were able to keep their memories intact. On the other hand, those who turned into demons were bothered by negative emotions, and as such, parts of their soul would remain within their corpse, making them lose the memories they had of their past life. These demons would only be able to recall their memories with continuous and fruitful practice, and even so, their recollection would only be in part while their characters would change dramatically.

Mitsue Natsume, You Dummy!