After having to deal with jealousy from his co-workers for working under his father's name, prideful literary editor Ritsu Onodera is determined to establish himself in the industry. To accomplish this, he quits his job at his father's publishing company and transfers to Marukawa Publishing. But instead of being placed in their literary division, Ritsu finds himself working as the rookie manga editor for the Emerald editing department, a team that operates under extremely tight schedules in order to meet deadlines. There, Ritsu is introduced to the infamous editor-in-chief Masamune Takano, a persistent man who strives for results. As it turns out, Takano is actually Ritsu's high school love, and it is the aftermath of that heartbreak has caused Ritsu's reluctance to fall in love again. Now with the two reunited after several years of separation, the reestablishment of their relationship is marked by Takano's vow to make Ritsu say that he loves him again. Sekaiichi Hatsukoi follows three couples that are interconnected within the manga industry, with each being subject to the budding of first love.

High school biology teacher Tetsuo Takahashi may look like your average everyday instructor, but beneath his gentle appearance lies something less ordinary: his fascination for the "Ajin," more commonly known as "Demi." Although these half-human, half-monster beings have integrated into human society, Takahashi believes that much about them will remain unknown unless he interacts with them firsthand. Demi-chan wa Kataritai follows Takahashi's daily life in Shibasaki High School together with his three Demi students—Hikari Takanashi, an energetic vampire; Kyouko Machi, a gentle dullahan; and Yuki Kusakabe, the shy snow woman. Along the way, Takahashi also meets fellow teacher Sakie Satou, a succubus with an aversion towards men. To fulfill his goal of learning more about the Demi, Takahashi decides to conduct casual interviews with the girls to learn more about their abilities, psyche, and interaction with human society. As Takahashi strengthens his bond with his students, he soon discovers that the Demi are not as unusual as he initially believed. [Written by MAL Rewrite]

In a dystopian future where Japan's political organization has crumbled after the Great Tokyo War, Japan is broken up into 10 independent nations, with each nation controlled by a gang led by a "Best," a human-proclaimed prophet with destructive superpowers. Nozomi Moritomo is a "Rest"—a normal girl that has just started out as a rookie in the local gang. She wants to help the Best Masami Utoku, her childhood friend and role model, in the ongoing territorial dispute. When Masami becomes severely injured and unable to fight, Nozomi decides to go on a mission to complete the requests sent to Masami from all over Japan. Along the way, she meets Yukina Kosaka, a shy girl with no sense of direction; Ai Hibiki, an upbeat girl who loves eating; and Chiaya Misono, a quiet and mysterious girl that wears a gas mask. Together, the four girls travel all over the country on their motorcycles while getting involved in territorial wars, disagreements, and even suspicious conspiracies. [Written by MAL Rewrite]

Following Armageddon, an apocalyptic war, mankind faces yet another menace: vampires. The continuous confrontations between the races have split the world into separate factions. The race of vampires, Methuselah, are affiliated with the New Human Empire; whereas the humans, deemed Terrans by the vampires, make up the Vatican Papal State. Furthermore, extremist groups like the Rosenkreuz Order strive to rekindle a war, despite the factions' attempts to avoid direct conflict. To combat terrorist organizations, the Vatican has implemented the AX unit. Led by Cardinal Caterina Sforza, the AX agents investigate vampire-related disturbances with hopes that the Terrans and the Methuselah will one day achieve a peaceful coexistence. Amongst the AX unit is priest Abel Nightroad—a seemingly disoriented but gentle-hearted fellow, and a fierce vampire slayer on the battlefield. Joining the unit as his partner is a new agent, Sister Esther Blanchett, a brave and gentle young nun troubled with a tragic past. As the two grow closer, they begin to uncover signs of malicious schemes and dark forces working in the shadows. But the path they walk is riddled with misfortune that might just force them to confront the memories that plague their hearts.