During his summer vacation, middle school student Nagasumi Michishio travels to the Seto Inland Sea. One day, while swimming at Mio Sun Beach, his leg suddenly cramps. No one is close enough to notice his desperate screams for help, and so he sinks into the ocean, where he is left to drown alone. Just as he loses consciousness, however, a mermaid appears and saves his life. That night, Nagasumi is visited by his savior, a girl who introduces herself as Sun Seto—a mermaid from a yakuza family. As it turns out, under mermaid law, a mermaid whose identity is revealed to a human must be punished by execution. To avoid this harrowing outcome, the Seto family propose a solution: Nagasumi must marry Sun or die at the hands of Gouzaburou, Sun's father and boss of the Seto clan. Faced with no other option, Nagasumi takes her hand in marriage. Now, the newlyweds face the difficult task of keeping their relationship secret. Between Gouzaburou's unending attempts on Nagasumi's life and the eccentric antics of a slew of antagonists, a genuine and innocent love blossoms between the pair as they adapt to their new life. [Written by MAL Rewrite]

In the kingdom of Forland, a coup d'etat occurs which leads to the death of the King. In the last moments of his life, the King sends his second child, Princess Alita Forland to escape. Unfortunately, while fleeing, a life and death situation between Alita and the bloodthirsty bounty hunter Falis causes the two of them to switch bodies. Desperate for the safety of her Kingdom, Alita begs Falis to return and protect the Kingdom, offering herself as collateral. After a swift beating on the rebel forces, Falis resumes the title of Princess of Forland, leading to the birth of the most savage princess in their land, the "Murder Princess."

After scaling Mt. Everest, mountain climbing partners Saruwatari Gorou and "Lostman" Jack F. Woodbridge see the ISA Space Station, and each vows to make the trek into outerspace. When Helium 3, a new energy source, is discovered on the moon, NASA forms a new project named "Nexus" to harness that energy for use on earth. This is the story of the two and the paths they take to see their dream become a reality in the quest to harness the next-generation energy source. (Source: ANN)

The everyday lives of the Minami sisters continue. Chiaki, the youngest, continues to call people idiots while worshipping her eldest sister. Kana, the middle, still can't figure out that Fujioka's feelings for her are a crush, not a grudge. Haruka, the eldest, still unknowingly avoids Hosaka's advances to invite her to the volleyball team, and after a long day of excitement, the sisters enjoy sitting at the table at their home. (Source: ANN)