Ryouta Sakamoto is unemployed and lives with his mother, his only real achievement being that he is Japan's top player of the popular online video game Btooom! However, his peaceful life is about to change when he finds himself stranded on an island in the middle of nowhere, with a small green crystal embedded in his left hand and no memory of how he got there. To his shock, someone has decided to recreate the game he is so fond of in real life, with the stakes being life or death. Armed with a bag full of unique bombs known as "BIM," the players are tasked with killing seven of their fellow participants and taking their green crystals in order to return home. Initially condemning any form of violence, Ryouta is forced to fight when he realizes that many of the other players are not as welcoming as they may seem. Teaming up with Himiko, a fellow Btooom! player, they attempt to get off of the island together, coming closer and closer to the truth behind this contest of death. [Written by MAL Rewrite]

Venturing into the wilderness, the skeptical Ryouta Murakami and the ambitious Kuroneko were on a quest to prove the existence of extraterrestrial life when a tragic accident occurred, reaping Kuroneko of her life and leaving Ryouta in a critically injured state. Ten years have passed since the disaster, and Ryouta is now living a normal life in high school. He vows to prove that aliens are real in honor of his late friend. A transfer student named Neko Kuroha unexpectedly arrives one day, bearing a striking resemblance to the late Kuroneko—even sharing a similar name. Most mysteriously, she seems to possess supernatural powers. As Ryouta takes more interest in Neko, he is drawn into a deadly world where dangerous scientists hunt magic-wielding witches that have escaped from their secret research laboratory. Neko is one of these escapees, but there are many others who are in similar situations, and it's up to Ryouta to protect them from their would-be captors. [Written by MAL Rewrite]

Manji is an infamous swordsman in feudal Japan who is known as the "Hundred Man Killer," as he has killed one hundred innocent men. However, there is something far more frightening than his ominous reputation: the fact that he is immortal. This is the handiwork of eight-hundred-year-old nun Yaobikuni, who placed bloodworms capable of healing almost any wound in Manji's body. To atone for his crimes, Manji resolves to kill one thousand evil men. Yaobikuni agrees to this proposal, saying that if he succeeds, she will undo his curse of immortality. Soon after this promise, Manji meets Rin Asano, a 16-year-old girl who requests Manji's assistance in killing those who slaughtered her parents. Initially reluctant, Manji refuses Rin's desperate plea. However, owing to her evident lack of strength, Manji changes his mind and agrees to protect Rin for four years. With this partnership set in stone, the two embark on a perilous journey of bloodshed, vengeance, and redemption, each to fulfill their own life's cause.

In the year 2021, a parasitic virus known as "Gastrea" infects humans and turns them into monsters. What is left of mankind now lives within the Monolith walls, walls that are made of Varanium, the only material that can hurt Gastrea. To counter the threat that the Gastrea pose, "Cursed Children"—female children whose bodies contain trace amounts of the virus which grant them superhuman abilities—officially called Initiators by the Tendo Civil Security, are given partners called Promoters, people who work to guide and protect the young Initiators. These teams of two are sent out on missions to fight the monsters created by the Gastrea virus and keep them at bay. Black Bullet revolves around the team of Enju Aihara, an Initiator, and Satomi Rentaro, a Promoter, as they go on missions to fight the growing threat of Gastrea in their hometown of Tokyo. [Written by MAL Rewrite]