Dogi✩Maji✩Memorium (Dogi Maji in short) is an RPG school dating sim where anyone who registers is pulled into the game world. (note: If you die in the game, you die for real). To leave the game, you have to win it.
The game itself is played on Gehenna Station, which could be a parody of the PlayStation.
The game is set in a fictional school, which seems to be in the human world. It has computer generated classmates and teachers whom with the players of the game can interact.
Note: this section may include spoilers
In Lesson 10, Mammon has the idea to register Satan and Lucifer to the game to make them work together in order to get out of it. Leviathan helps Mammon in registering them, but also registers himself and MC as well. He also registers Mammon as "Stupidmammon."
MC is registered as the heroine — a title unrelated to MC's actual gender — and Lucifer, Mammon, Leviathan and Satan have to increase their favorability score with her in a similar manner to how players raise intimacy scores with the main characters.
The game can only be won if MC as the heroine receives a confession of love on the Roof of Legend that they then accept.