Dogi✩Maji✩Memorium

Doji ⭐Maji⭐Memorium (Doji 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.

Mammon originally had the idea to register Satan and Lucifer to the game to make them work together in order to get out of it. (Lesson 10)

Leviathan helps Mammon registering them, but since he wanted to play this game for so long, he registered himself as "Leviachan". Then invites MC as well and Mammon follows along (and he's being registered as "Stupidmammon" by Levi).

Setting
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.

Plot
In Lesson 10, MC is registered as the heroine (unrelated to MC's actual gender or appearance) and Lucifer, Mammon, Leviathan and Satan have to increase the favorability score with her (like how you raise the intimacy with the brothers).

They can only win the game if they confess their love to the heroine on the Roof of Legend and she accepts it.

Trivia

 * It's mentioned in a conversation between Mammon and Leviathan that version 2.10 of the game has a bug that makes the whole game crash, so the Developers of the game recalled the whole batch.