Long ago, alien lifeforms came to Earth, fusing with people on the planet. Due to their appearance, they were dubbed "Mecha-ude," as when fused, they bore a striking resemblance to mechanized limbs. Through an involuntary partnership, average middle schooler Hikaru Amatsuga works alongside the Mecha-ude Arma, who is an extremely rare and special existence. To protect Arma, the resistance group ARMS assigns the dual Mecha-ude user Aki Murasame to follow him wherever he goes. However, she is also looking for a mysterious Snake-Type Mecha-ude wielder, who has put many of her comrades in a critical state. Behind the scenes, an organization known as the Kagami Group is searching for the mythical "Trigger Arm," a Mecha-ude said to grant unlimited power. When Aki's life is threatened by this group, Hikaru must team up with Arma to find the courage to fight back and, along the way, learn that his life will never be ordinary again. [Written by MAL Rewrite]

Yoshino Somei would have been a normal high-schooler if not for the fact that she is the granddaughter of the leader of the Osaka-based Somei Group, the Kansai region's largest yakuza organization. One day, Yoshino hurries home after hearing of the news about the unification of Kansai and Kanto's biggest syndicates, the Somei and the Miyama groups. This, according to the article, will result in a marriage of the leaders' grandchildren—one of whom is Yoshino herself! Despite her best efforts to annul the arrangement, Yoshino has to go to Tokyo to visit her fiancé, Kirishima Miyama, who is unexpectedly nice and charming. During their first meeting, Yoshino is swept up in various events and becomes unable to refuse moving to Tokyo, which is why, half a year later, she now lives with the Miyama group. At school, she soon realizes that Kirishima is very popular, so her relationship with him garners the hate of his fangirls and subsequently results in bullying. To make matters worse, Kirishima could not be further away from her prince charming since he, after all, was born to be a yakuza member. follows Yoshino and her new life in Tokyo that is filled with nothing but troubles connected to the underworld. However, though she wishes to be as far from it as possible, this isn't Yoshino's first time dealing with the world of the Yakuza... [Written by MAL Rewrite]

Hitoyoshi Yokoya is a high school student who currently lives alone. One day, an unfamiliar girl knocks on his door and offers to be his maid. She reveals that she is a former assassin, which makes Hitoyoshi nervous. But when her skills save him from being run over by a truck, Hitoyoshi ultimately decides to take her in. However, the mysterious girl actually has no household skills. In fact, her only expertise is assassination, as she has lived her entire life for the sake of killing. Nonetheless, her time with Hitoyoshi allows her to experience new emotions she had never felt before, inspiring her to become a regular girl. In order to advance toward this upcoming chapter in her life, she asks Hitoyoshi to grant her a new name, to which he names her Yuki. Having someone she can finally consider family, Yuki acquires new fond memories that fill her heart with warmth as she tries to leave her dark and lonely past behind. [Written by MAL Rewrite]

The story follows a group of five in a world where people have suddenly disappeared. A mysterious self-proclaimed "Emperor" gathers five people together through anonymous messages and has them participate in a game. Participants answer the question "Do you want to live or die?" The game has only one rule: "Majority dies."