In the year 1930, vampires have infiltrated Tokyo to feast upon its unsuspecting citizens. As the number of victims continues to rise, the city's authorities decide to hire the Jaegers—a strange, diverse group of individuals tasked by the V Shipping Company to hunt down vampires around the world. Carrying musical instrument cases to disguise their identity, the Jaegers battle the vampires with the same mercilessness demonstrated by their foes. Yuliy, the Jaeger's most skilled warrior, is the sole survivor of a vampire raid on his home village. Using the strength granted by his werewolf blood, he works with his team to assist Tokyo's law enforcement with the city's vampire problem. Though under the pretense of helping the police, the Jaegers are actually fighting the vampires over the mystical Ark of Sirius. With its power to change the fate of the world, Yuliy and his friends must locate the artifact before the vampires can use it to achieve their destructive goals.

Thirty-seven-year-old Satoru Mikami is a typical corporate worker, who is perfectly content with his monotonous lifestyle in Tokyo, other than failing to nail down a girlfriend even once throughout his life. In the midst of a casual encounter with his colleague, he falls victim to a random assailant on the streets and is stabbed. However, while succumbing to his injuries, a peculiar voice echoes in his mind, and recites a bunch of commands which the dying man cannot make sense of. When Satoru regains consciousness, he discovers that he has reincarnated as a goop of slime in an unfamiliar realm. In doing so, he acquires newfound skills—notably, the power to devour anything and mimic its appearance and abilities. He then stumbles upon the sealed Catastrophe-level monster Storm Dragon Veldora who had been sealed away for the past 300 years for devastating a town to ashes. Sympathetic to his predicament, Satoru befriends him, promising to assist in destroying the seal. In return, Veldora bestows upon him the name Rimuru Tempest to grant him divine protection. Now, liberated from the mundanities of his past life, Rimuru embarks on a fresh journey with a distinct goal in mind. As he grows accustomed to his new physique, his gooey antics ripple throughout the world, gradually altering his fate.

As the Mars expedition comes to an end, a small group of Terraformars manage to reach Earth and bring the fight there. Now the surviving members of the ANNEX-I along with new recruits, have to save Earth from the growing roach menace. (Source: AniDB)