I really like the thought of MC's interactions and relationships with the other beings in Devildom. The demon bros and rest of the cast are great but I feel like it's the little interactions with the 'NPCs' that would make Devildom worth staying in and feel more... organic. There's a group of succubi for MC to party with at the Fall when Asmo gets too much to handle for the night. A retailing demon at Majolish that knows which new releases will suit MC whenever they drop by. A demon at Hell's Kitchen that knows MC's order off by heart. A witch that gives MC discounts on potions and hexes just because they're a regular.
It's canon that MC is pretty popular at R.A.D., there are lesser demons regularly greeting MC in the hallways and likely jump at the chance to give MC their pen if they ever forget. Members of the Fangol team keep MC company as they wait for Beel to finish up. MC has made friends with the demons who have their lockers next to them, they have conversations before school every morning.
And it's not just the humanoid creatures. Cerberus is a given, becoming more of a supersized puppy whenever it sees MC, much to Lucifer's chagrin. A haunted portrait painting in the castle will break into a grin whenever MC walks past. There's a Little D that hovers around MC whenever they go to Diavolo's castle, it was so preoccupied with trailing after MC it almost left the castle entirely when they did.
