A runaway vehicle driven by Izumi Yasaka, en route to the Public Safety Bureau building, is reported shortly before it crashes into the building. Izumi is a counselor who recently ran away while working at a latent criminal isolation and rehabilitation facility known as Sanctuary. Before Inspectors Mika Shimotsuki and Akane Tsunemori get to interrogate the suspect, a sudden request is issued from the facility to promptly bring Izumi back. Interpreted as a direct order from the Chief and the board at Sanctuary, the Inspectors obey, but insist that Izumi be escorted back personally. Tsunemori intends to investigate further with the rest of the team at the Bureau. Now Inspector Shimotsuki has finally been given the opportunity she had been waiting for—to be the primary investigator on an important case. This case follows Shimotsuki and her team of Enforcers as they uncover the secrets of Sanctuary.

The village of Ootsuka—home to Shino Inuzuka, Sousuke Inukawa, and Hamaji—was lit on fire under the preconception that a virus had seen all of its life eradicated. Now surrounded by flames and on the verge of death, the three were approached by a strange man holding a sword. He tells them that they must reach a decision if they want to live. That night changed everything for these children. Five years later, the family of three now lives under the watchful eye of the small Imperial Church in a nearby village. All is fine and dandy until the Church attempts to reclaim the demonic sword of Murasame. To accomplish this, they kidnap Hamaji to lure Shino, now a bearer of Murasame's soul, and Sousuke, who possesses the ability to transform into a dog. The brothers must put their differences aside to rescue their beloved sister from the Church in the Imperial Capital, signalling the beginning of a very difficult journey.

On his way home from school, Tatsumi sees a man collapsed near a lake. When he approaches him, Tatsumi notices something strange: the person in need of help is actually a beautiful merman named Wakasa! Because Wakasa's home has become too polluted to live in, Tatsumi graciously offers his bathtub as a refuge. With a boisterous merman as his new roommate, Tatsumi's normal life won't be returning anytime soon, not to mention Wakasa's aquatic friends—Takasu, Mikuni, and Maki—often show up uninvited, making them all quite a handful for the high school student. As he humors their curiosity for human life, Tatsumi sometimes finds himself enjoying their childish antics, but he will have to keep his cool if he intends to keep up with his daily life and newfound friendship. [Written by MAL Rewrite]

Hayate Ayasaki's misfortune continues to hand him the short end of the stick. Now settled into his routine at the Sanzenins' mansion and Hakuou Academy, the butler continues to work as hard as ever in caring for his young mistress Nagi while studying the school's grueling curriculum—all on top of trying his best to survive the multitude of troubles that life relentlessly pushes onto him. The unintentional chick magnet's life is far from quiet, forced to deal not only with Nagi's yet unnoticed infatuation with him, but also the evergrowing string of accidentally seduced girls—most notably, the exceptionally plain Ayumu Nishizawa, a friend of his before he became a butler, and the diligent Hinagiku Katsura, Hakuou's student council president. While one struggles to gain his affection and the other desperately tries to deny her own, both the girls are going to make the boy's life a little more complicated than it already is. [Written by MAL Rewrite]