Hellsing, an organization specializing in dealing with supernatural threats, is called in to eliminate a vampire that is turning the villagers of Cheddar into ghouls. To put an end to this, the leader of the organization, Sir Integra Fairbrook Wingates Hellsing, dispatches her most formidable asset: a powerful vampire known as Alucard. Armed with only a single handgun, Alucard wreaks havoc on the monsters plaguing Cheddar. However, a young police officer, Seras Victoria, gets caught up in the chaos and becomes mortally wounded as a result. Taking pity on the girl, Alucard gives her a choice: die as a human or live on as a vampire. Seras accepts his offer and begins a new life as a member of Hellsing. Though it was her decision, Seras struggles with the fact that she is no longer human. Nevertheless, she must embrace being a creature of the night soon if she wants to survive on the front lines in the fight between humans and the supernatural.

Running into your new stepsister in the bathroom is not the best way to make a good first impression, which Basara Toujou learns the hard way. When his father suddenly brings home two beautiful girls and introduces them as his new siblings, he has no choice but to accept into his family the Naruse sisters: busty redhead Mio and petite silver-haired Maria. But when these seemingly normal girls reveal themselves as demons—Mio the former Demon Lord's only daughter and Maria her trusted succubus servant—Basara is forced to reveal himself as a former member of a clan of Heroes, sworn enemies of the demons. However, having begun to care for his new sisters, Basara instead decides to protect them with his powers and forms a master-servant contract with Mio to keep watch over her. With the Heroes observing his every move and the constant threat of hostile demons, Basara has to do the impossible to protect his new family members. Moreover, the protector himself is hiding his own dark secret that still haunts him to this day...

Apparitions, oddities, and gods continue to manifest around Koyomi Araragi and his close-knit group of friends: Tsubasa Hanekawa, the group's modest genius; Shinobu Oshino, the resident doughnut-loving vampire; athletic deviant Suruga Kanbaru; bite-happy spirit Mayoi Hachikuji; Koyomi's cute admirer Nadeko Sengoku; and Hitagi Senjougahara, Koyomi's eclectic girlfriend. A new semester has begun and with graduation looming over Koyomi, he must quickly decide the paths he will walk, as well as the relationships he will form and friends that he will save. But as strange events begin to unfold, Koyomi is nowhere to be found, and a vicious tiger apparition has appeared in his absence. Hanekawa has become its target, and she quickly finds she must fend for herself.

Seiya Kanie, a smart and extremely narcissistic high school student, believes that the beautiful but reserved Isuzu Sento has invited him on a date at an amusement park called Amagi Brilliant Park. Much to his chagrin, not only is the location a run-down facility, the supposed date is merely a recruitment tour where Sento and Princess Latifa Fleuranza, the owner of the theme park, ask him to become the park's new manager. Their cause for desperation? As stipulated in a land-use contract, Amagi has less than three months to meet a quota of 500,000 guests, or the park will be closed for good and the land redeveloped by a greedy real-estate company. Seiya is won over by the revelation that Amagi is no ordinary amusement park; many of its employees are Maple Landers—mysterious magical beings who live in the human world and are nourished by the energy created by people having fun. Entrusted with the hopes and dreams of this far-off enchanted land, Seiya must now use his many skills to bring Amagi back on its feet, or watch it crumble before his eyes.