Files of the Unknown: Irrationality! Unreasonable!

[If you cannot accept a protagonist who is inhuman, abnormal, loves to complain, and whose gender is unknown, or you are unable to accept the pitfalls and are too slow to fill in the gaps, please leave the first-person perspective and a bit sloppy plot. Prelude: Whatever doesn't kill me will make me stronger! Postposition: I am immortal, no one can kill me... The theory has been established. Death is just a new beginning for me. If I fall down a hundred times, I will stand up a hundred and one times with stronger strength. Abandoning memories and forgetting the past is not to escape or to start over. I help them complete their ultimate project, and they help me become... An existence. This is a "friendly" deal for both parties.