Yuuichi Katagiri believes that friends are more important than money, but he also knows the hardships of not having enough funds. He works hard to save up in order to go on the high school trip, because he has promised his four best friends that they will all go together. However, after the class' money is all collected, it's stolen! Suspicion falls on two of Yuuichi's friends, Shiho Sawaragi and Makoto Shibe.
Soon afterwards, the five of them are kidnapped, and wake up in a strange room with a character from a short-lived anime. Apparently, one of them has entered them into a "friendship game" in order to take care of their massive debt. But who was it, and why did they have such a debt? Could they have stolen the money from class to pay for entry into the game? Yuuichi and his best friends will have to succeed in psychological games that will test or destroy their faith in one another.
When it comes to the fantasy MMORPG Cross Reverie, none can match the power of the Demon King Diablo. Possessing the game's rarest artifacts and an unrivaled player level, he overpowers all foolish enough to confront him. But despite his fearsome reputation, Diablo's true identity is Takuma Sakamoto, a shut-in gamer devoid of any social skills. Defeating hopeless challengers day by day, Takuma cares about nothing else but his virtual life—that is, until a summoning spell suddenly transports him to another world where he has Diablo's appearance!
In this new world resembling his favorite game, Takuma is greeted by the two girls who summoned him. They perform an Enslavement Ritual in an attempt to subjugate him, but the spell backfires and causes them to become his slaves instead. With the situation now becoming more awkward than ever, Takuma decides to accompany the girls in finding a way to unbind their contract while learning to adapt to his new existence as the menacing Demon King.
The Hidden Dungeon is a place of legend where rare treasures and items are hidden. Nor, the third son of an impoverished noble family who's lost the one job offer he had, was lucky enough to hear about this dungeon. He then acquires a skill that allows him to create, bestow, and edit skills... and in order to use it, he needs to accumulate points by carrying out such tasks as eating delicious meals and doing sexual things with alluring members of the opposite sex.