Tsukasa Atsumi is a salaryman who leads an ordinary, solitary life. On his way back from work one evening, he is saved from a demon attack by a mysterious woman in a ninja outfit. Introducing herself as Shizuri Ideura, she claims that demons target people like Tsukasa, who have Samurai Blood in their veins, and that her kind have been protecting them from the shadows. Told by Shizuri that the attacks are going to become more frequent, Tsukasa makes a deal to provide her with housing in exchange for his safety. To his surprise, he quickly finds out that Shizuri is a shut-in who loves to play video games whenever she is not busy with her ninja duties. As the two spend more time together, Tsukasa grows to appreciate Shizuri's company—and his feelings just might be mutual.

Surrounded by four armies of dark beasts, five humanoid races strive to push the known boundaries of the world. Unfortunately, the 13 heroes dispatched to the southern region are easily wiped out by Clevatess, one of the Lords of Dark Beasts. Determined to get revenge against humanity, Clevatess bursts into the capital of the Kingdom of Hiden, leaving a trail of death and destruction behind him. Although the situation looks desperate, humanity still has a chance to appease Clevatess' anger. Alicia Glenfall, one of the 13 heroes, is revived by Clevatess to help him raise a newborn infant, Luna, whose choices shall shape the fate of the human world. Although reluctant to help the dark beast at first, Alicia understands that Luna is the only thing that stands between humanity and complete annihilation. Hiding himself by taking on a human form, Clevatess sets out in search for a wet nurse with Alicia and Luna. With Clevatess unwilling to reveal his identity, it falls on Alicia to slay all enemies that stand in their way. Meanwhile, the neighboring countries prepare to advance on the weakened Hiden, aiming to control the only forge capable of producing the heroes' weapons.

University is back in session for Iori, and so are the booze-fueled parties! Between diving club shenanigans, a surprise from his sister, and wild tests of courage, normal college life is anything but. Dive back into the madness with Iori and his beloved crew of lively splash artists.