Death. Death had many misconceptions by the living. Nobody discussed how people continued average lives post-death. People never gossiped about how somebody was destined for a trashy apartment when they died. Shower thoughts about the billions of Underworld residents didn't irritate humans, but they nuanced the dead.
That's what Theo was. He was a being cursed with an eternal afterlife full of lusterless loneliness. After he died, his expectations were quickly disproven. Being good wasn't enough in the Underworld; you had to do something significant to deserve anything.
Theo was passed to the grim depths of nobodies with three things: an apartment key, clothes, and a morsel of sanity. He trudged to his apartment with dwindling optimism.
As he learned to manage, his hope only lingered within the rules he set. He refused to go upstairs, visit the town, or talk to anyone except the depressed market worker, who he was sure was a figment of his imagination. There wasn't ever a need to break the restrictions keeping him safe. However, change is inevitable.
Theo was returning from the market when he spotted someone in his dim apartment hallway. Nobody lived on floor 57 except him. An unfamiliar sensation twisted his insides. They looked no older than him, so he carefully continued. Theo made sure to note every detail about the person. After all, nobody knows when someone is out of their mind. He noticed a little dangling key in the other's hand. It was true: a new resident was on his floor.
Theo attempted to ignore the person, but the sight of shaky and sweaty hands caught his eye. He was like that when he first arrived in the Underworld. A shadow of guilt darkened his face, and he narrowly decided to overcome his cowardice.
He approached who he assumed to be his newest neighbor and gently took the key out of their hand.
"You must be new here," he meekly greeted, "Welcome to the Underworld."
It took a couple of tries, but he eventually got the door unlocked for them. He gave a proud smile.