[Hopeful Death]

Spoiler for Kakeru the druggie:

I remember him explaining that it was a special rare type of LSD that he said was used in some third world country in ceremonies and it had the effect of altering your personality, and he tried using it constantly in the hopes that eventually the 2nd personality born from the use of the drug would 'stick' and eventually he wouldn't need to use the drug to make that personality appear. He did it because he was envious of the protagonist's condition and wanted to duplicate it himself(so he could forget his painful memories like the protagonist did)

Pretty sure that conversation was cut from the anime? I don't remember, I assume it was considering these questions

As a little side note, I guess I should note that the anime made it pretty obvious Kakeru had a point of contact with the protag in the past that they never clarify. That point of contact being that

Spoiler for contact and the birth of Garuda:

he and Garuda were in the same mental institution for a short period of time when they were children. After Youji retreated into his psyche, the 'body' basically just became a beast of rage and violence with no personality, at that point he was sent to an institute, and that personality-less beast eventually formed intellect as it stayed there, which would go on to form into the personality we know as Garuda. Unfortunately the personality it formed was based on all the knowledge of Wing Quest that was hanging around in his brain.