idk if this has been brought up yet, but whatever.
Famicom world (Underworld) is hell. She associates it with Famicom because seriously fuck NASU and all that it stands for. Have you ever been SO pissed at a game that you feel like a volcano is exploding inside you and assaulting all your nerves? Like you're suddenly channeling the angry video game nerd? Yeah kinda like that.
Strangely, despite Oni being ogres/large imps/not-demons, the purple oni seems to be more of a devil. His house is full of file cabinets, has something akin to a lobby, and he can teleport to the Underworld.
The Oni could represent someone she knew and thought cruel enough to consider a devil; it could be something as benign as an asshole brother who affectionately ruins her life (as evidence by the whole "house" thing and the gentle, childlike music that plays in his room), or some druggie/delinquent.
Since the demon teleports her out of the Underworld if she talks to him, he could be quite fond of her, or has previously pulled her out of a hellish period in her life.
His sprite is pretty angry so I'd imagine he's tsundere or has a scary face.
Basically, unrelated issues clashing together in the confusion of a dream.