Shintarou Tokumitsu leads an ordinary high school life while living in a studio apartment just for himself. This changes drastically one morning after he finds something strange on his balcony—an angel from Heaven. The innocent and kind girl named Towa was sent to Earth by God to learn more about humans and their way of interacting. It does not take long for her to get attached to Shintarou, who eventually allows her to live with him. However, the small apartment provides little personal space and privacy, and hiding Towa's real identity from the public proves difficult. As he learns to navigate his new life with Towa, Shintarou's encounters with other girls may only complicate the circumstances.

Hikaru Amatsuga's days of tranquility come to a sudden end when he rescues Alma, a mechanical arm crying for help. Alma fuses with his jacket, introducing Hikaru to the world of mechanical arms: mysterious, sentient weapons that normally become a part of their users' bodies. Forced to flee for his life, Hikaru is eventually captured by Aki Murasame, a twin mechanical arms user working for ARMS, an organization that protects the machines against unethical treatment. The Kagami Group, a nefarious organization that treats mechanical arms as mere tools, seeks to recover Alma. Hikaru is deemed a failure by ARMS for his lack of natural predisposition to be an mechanical arm wielder, so Aki is assigned to be his bodyguard. But Aki is defeated by Jun Kagami, who cruelly tears out her two mechanical limbs, condemning the girl to a slow death. Unwilling to abandon Aki to her grim fate, Hikaru miraculously awakens his power and neutralizes Kagami. Now a full member of ARMS, Hikaru is determined to unravel the truth about mechanical arms and protect his newfound friends and allies.

Jill Savelle—fiancée of the crown prince Gerald der Kratos and known as the Lady Goddess of War—is being hunted down by the same country she swore to protect. Betrayed by her betrothed, she is framed as a traitor and imprisoned. In her last moments, Jill is filled with regret, but just as death approaches, she awakens six years in the past. This time, she will not be a mere pawn. Now as a 10-year-old girl, Jill resolves to escape her imminent engagement to the prince. To this end, she jokingly professes her love to the 19-year-old dragon emperor Hadis Teos Rave, who will one day stain the land in blood due to madness. But against all expectations, he accepts! In contrast to the tyrant from Jill's memories, the Hadis of this time is a kind albeit unfortunate emperor. Can Jill prevent Hadis from descending down the same dark, villainous road, or is he bound to an inevitable future?

Returning from their summer vacation, the students of Class 3-E at the prestigious Kunugigaoka Middle School find themselves up against unbeatable odds. Faced with the possibility of world annihilation, the students must come up with increasingly elaborate and creative ways to kill their teacher, the cunning yet optimistic and helpful Koro-sensei. However, eliminating Koro-sensei is not the only objective the students need to worry about. Gakuhou Asano, the academy's merciless and cruel principal, seeks to prevent Class 3-E's success by brainwashing his other hard-working pupils into ruthlessly competitive studying machines. Hostility begins to linger in the air as traitors and killers alike attempt to claim the bounty on Koro-sensei's head for themselves. Nagisa Shiota, one of Class 3-E's most skilled assassins, finds himself in the middle of the conflict. While he works to maintain his academic standing and prevent the end of the world, domestic affairs jeopardize his place in Class 3-E. Together with his dedicated classmates, he must now face the threats head-on.