The story is about the inhabitants of the fictional town of Hamburg, locked in a castle in quarantine. William, the Messenger who brought the news of the plague, is also locked up in the castle.

One day, high-school boy Yamada bumps into the beautiful girl Shiraishi on the stairs (literally), and their lips touch as they fall. When they regain their wits, they realize that they have swapped bodies. As time progresses, the two realize that this is not the only mysterious happening in the school.

While job hunting, Naoya is taken by a mysterious girl to a magical land where he is installed in the harem of the succubus Princess Lotte. Thanks to trauma from her childhood, Lotte hates men and surrounds herself with lots of other women, who all have quirks of their own. In spite of her selfishness, when Naoya learns that Lotte is really quite lonely he agrees to stay in her world...if he can bring his daughter Asuha with him.

Yuuya Nomoto was horrified to discover that the vehicle he was driving was being used to kidnap a high school girl, but he's even more shocked when the girl, Hitomi Uzaki, literally tears her kidnappers to pieces instead! Then she forces Yuuya to drive her to an arena where she bets the value of his organs on herself to win in a death match against a half-lion hybrid! Even more astonishing: Hitomi wins! That's because she's a Therianthrope, a genetically engineered fighter created specifically for the underground death matches known as Killing Bites! And now that Yuuya has been pulled into this dark underworld, he has no choice but to continue working for Hitomi. Because who's going to fight against a girl who's part honey badger?

Hida Kizuna possesses the HHG (Heart Hybrid Gear) ability, but it is not strong enough to make him particularly important. His older sister calls him to transfer to a strategic defense school, where many of the students (many of which are large-breasted girls) use their HHG abilities to fight invaders from another world while wearing extremely skimpy pilot outfits. Kizuna's fighting ability doesn't measure up, but his sister has another plan—apparently having erotic experiences with Kizuna will allow the girls to replenish their energy or power-up. It looks like his new school life is going to be full of embarrassment.

Hitori Bocchi, a girl with extreme social anxiety, has had only one friend throughout elementary school. When Bocchi learns they'll be split up after graduation, she makes a promise to her: "By the time of my middle school graduation, I'll make friends with everyone in my class." And if she can't... they won't be friends anymore?! But Bocchi has a hard time talking to people. When she gets nervous, her legs cramp. She can't look other people in the eye. She doesn't even know how to make friends! Every way she thinks of to make friends ends up failing. Will her friend-making plan pay off?!