When Mr. Crawling first entered the ghost realm, he had no idea he died. He still had memories surrounding his death, but it felt more like waking up than fading away.
He quickly lost even these memories, and forgot about being human altogether.
Given he still doesn't know he's dead, he doesn't think of himself as a ghost. He's a resident of the apartments -- and he doesn't think of the ghost apartments as apartments. it's just where everyone is. Despite being pretty smart, he just doesn't have the context for any of this to make sense.
My Mr. Crawling background concept. I spend a lot of time over-explaining things and then never get around to actually telling people my ideas... So here's me getting it out quickly + quietly. Warning for abuse and sadness!
to put it simply, he's a Yūrei. Spirit barred from a peaceful afterlife, trapped between worlds kind of thing.
"[...]However, if the person dies in a sudden or violent manner such as murder or suicide, if the proper rites have not been performed, or if they are influenced by powerful emotions such as a desire for revenge, love, jealousy, hatred or sorrow, the reikon is believed to transform into a yūrei which can then bridge the gap back to the physical world." (wikipedia)
he died in the Heian period, having been born into a family of wealth to royals, only to have been neglected and left to die alone in a room no one was allowed access to. They were ashamed of him for being disabled, having been born without sight and being born mostly deaf. even more so because he was their only son, the son they had been waiting for after two daughters. his family hid him, never allowing the people to know of him, not wanting their family name associated with him or him to have power over their legacy.
he wasn't taught things, he had no intimate connections or even platonic bonds. Not even his sisters cared very much for him. He died young, but lived longer than most would have in his position. They didn't intend on killing him, but he was emaciated and forgotten.
I started thinking a lot about what his backstory could be after having seen this, you can tell I took some inspiration!
the emotion that drives him isn't vengeance, it's not entirely sorrowful either. it's definitely sad, but not all encompassing. but he feels very protective over the weak and vulnerable, or those he percieves to be weak and vulnerable. he's driven by a need for purpose... forever wandering until he finds it, maybe he never will. or maybe he'll never be able to fulfill it, even with it right there...
