>>14974259I think Reaper candidates are chosen from a young age and come from normal Underworldian families. There's no specific look to the denizens of that world, Mori has said she's a skeleton who chose a human body.
Maybe Mori stood out immediately to Death-Sensei or maybe he noticed her potential on his own as she trained in classes. I think he challenged her with tougher assignments than other, and eventually as he took her on as his apprentice (while other Reapers did the more regular work) she had built a close bond with him. She still has her family but her mentor is someone special to her.
Maybe there was even a time, or test, where Death-Sensei said "Working with me means you will never see them again." to see how she would react.
