Sekai-Ichi Hatsukoi: Onodera Ritsu no Baai (世界一初恋 〜小野寺律の場合〜?, lit. "The World's Greatest First Love: The Case of Onodera Ritsu") is a Japanese boys-love manga series written and illustrated by Shungiku Nakamura.
Sekai-ichi hatsukoi traces the story of four couples (two are covered in the manga and the other two are presented as novels). Some of the characters know each other and all have in common publishing and books in general.
Sekaiichi Hatsukoi - Onodera Ritsu no Baai
Onodera Ritsu leaves the publishing house of his father for Marukawa Shoten. To his great misfortune, he who wanted to take care of the department of literature, is assigned to the department of mangas shōjō, things that he hates. He begins seriously to consider his departure nearest, because his boss, Takano Masamune, tackles him more and more on the nerves. However, the latter managed, by calling it "useless" to convince Onodera to perfect his work. The story takes a completely different turn when Ritsu learns the old name of Masamune: Saga, who turns out to be a former classmate to whom the latter had confessed his love at the time.
Onodera Ritsu no Baai is the most developed story in manga and anime.
Ritsu Onodera (小野寺 律 Onodera Ritsu?)
Ritsu Onodera is a 25-year-old jaded literary editor. He is the only son of the head of Onodera Publications, previously working at his father's company in the literature department. Hearing his fellow co-workers accusing him of only getting ahead due to his father's influence, he decides to show that he can be successful on his own by going to work at Marukawa Publishing. After being hurt by his first love in high school when he was 15, Onodera vowed to never fall in love again. His resolve is tested, however, when he is reunited with the boy he once loved, Masamune Takano. With Takano now very much a man and his new boss, things become very complicated for Onodera as he must juggle his career and his feelings for his first love.
Before transferring to Marukawa Publishing, Onodera was an editor in charge Ryouichi Sumi, father of Misaki's friend Keiichi Sumi (also from Junjou Romantica).
Masamune Takano (高野 政宗 Takano Masamune?)
The 27-year-old Masamune Takano, formerly known as Masamune Saga before his parents' divorce and his mother's remarriage, is the editor-in-chief of the Emerald department at Marukawa Publishing, where he is sometimes referred to as "the Capable." He and Onodera were once in a brief relationship in high school, but split up over a misunderstanding. It is later revealed that, during college, Takano went through a breakdown from his breakup with Onodera, family problems, and other personal issues, which in turn left him with unresolved feelings for Onodera. When both he and Onodera realize who each other are, he promises Onodera that he will make him fall in love with him again, much to Onodera's contempt.
In Sekai-ichi Hatsukoi: Takano Masamune no Baai (lit. "Masamune Takano's Case"), the reader sees Takano's perspective on his and Onodera's first meeting and romantic development.
Sekaiichi Hatsukoi - Yoshino Chiaki no Baai
Yoshino Chiaki is a mangaka, author of shōjō who writes under the pseudonym of Yoshikawa Chiharu. His editor, the best of the Emerald team of the Marukawa publishing house, is none other than Hatori Yoshiyuki, one of his old childhood friends. If Chiaki does not know that the latter loves him in secret, he is just as ignorant as another friend, Yanase Yuu, also has a crush on him.
Sekaiichi Hatsukoi - Yoshino Chiaki no Baai is the couple that is not tackled in Shungiku Nakamura's manga series. Their story is indeed related in novels, whose author is not Shungiku Nakamura, but Fujisaki Miyako. Shungiku Nakamura "merely" illustrates the books.
Chiaki Yoshino (吉野 千秋 Yoshino Chiaki?)
Chiaki Yoshino is a 28-year-old shōjo manga artist known under the pseudonym Chiharu Yoshikawa (a female name). His editor in-charge is Hatori Yoshiyuki, who is also his childhood friend. His two best friends are Hatori and Yuu Yanase, but the lines between friendship and love begin to blur after a number of confusing incidents. Yoshino begins to question his feelings for Hatori after witnessing him and Yanase together in what he thinks is a kiss; then Hatori kisses him one night and confesses his feelings. Yoshino begins to realize he has to confront his true feelings or risk losing them both.
Yoshiyuki Hatori (羽鳥 芳雪 Yoshiyuki Hatori?)
Hatori, also known as Tori, is 28 years old and an editor in Marukawa's Emerald department. Although in the beginning he is seen as serious and reserved, it is later revealed that he has secretly harbored deep feelings for his childhood friend, Yoshino. After confessing his love, Hatori pulls away fearing that Yoshino doesn't feel the same, who he believes loves his rival, Yanase, instead. However, unbeknownst to Hatori, Yoshino does somewhat return those same feelings.
Sekaiichi Hatsukoi - Kisa Shôta no Baai
Kisa Shôta, publisher in the Emerald team of Marukawa Publishing, fell in love with the bookstore of Book's Marimo. Unfortunately, Kisa is accustomed to always having unrelenting relationships with people he has just met. He systematically despises when he realizes that the object of his desires is not as perfect as he thought. But this time may well be the exception that confirms the rule, for it is the first time he falls in love.
Shouta Kisa (木佐 翔太 Kisa Shōta?)
Kisa is a fellow editor in the Emerald department and 30 years old, though he is usually mistaken for being much younger due to his looks. He considers himself gay but has never been in a serious relationship; in fact, he doesn't think himself capable of being in one because of his tendency to fall for a guy's good looks without knowing their personality. Because of this, he immediately questions his feelings for Kou and doesn't hold out much hope for a relationship with him. His mentality can be described by his line, "Love at first sight works well enough in manga, but this is reality."
Kou Yukina (雪名 皇 Yukina Kō?)
Kou Yukina is a 21-year-old clerk in charge of the shōjo manga section at the popular bookstore, Marimo Books. He's been aware of Kisa coming in to watch him, though he initially believed Kisa was just a shy high school student. When he discovers that Kisa is the editor behind all of his favorite works, however, he begins to develop romantic feelings for him, despite considering himself straight prior to their meeting. Throughout their relationship, Kou shows that he is more than willing to fight for Kisa, whom he tries to make understand that what they feel for each other is real and whom he believes to have the capability to fall in love.
Sekaiichi Hatsukoi - Yokozawa Takafumi no Baai
In the movie: Yokozawa Takafumi has been rejected by his best friend, Takano Masamune, of which he is madly in love. Dejected by this disappointment in love, Yokozawa isolates himself in a bar and drinks to excess. The next morning he wakes up in a hotel room. With him, Kirishima Zen, editor of the manga "The Kan" and the editor of Japun, a shonen manga magazine. Following an altercation between the two men, Yokozawa finds himself embarked in the personal life of Kirishima; Even going to take care very often of his daughter, Kirishima Hiyori. It is in this rather ambiguous relationship that Yokozawa Takafumi falls, despite his reluctance, under the charm of Kirishima ...
Although Yokozawa Takafumi appears in manga and anime, his relationship with Kirishima is discussed in the series of novels Sekaiichi Hatsukoi - Yokozawa Takafumi no Baii. The novels are also written by Fujisaki Miyako and illustrated by Shungiku Nakamura.
Takafumi Yokozawa (横澤隆史 Yokozawa Takafumi?)
Yokozawa works in the sales department at Marukawa. He is a close friend of Takano's, with whom he had a physical relationship when they were both in college. It is common knowledge in the publishing world that Yokozawa helped Takano get into publishing and his position at Marukawa. He is seriously jealous of and resents Onodera, whom he blames for "screwing up" Takano ten years ago. He often warns Onodera away from Takano, even going as far as proclaiming Takano is his.
He has his own side story entitled Takafumi Yokozawa No Baai about his new love interest, Kirishima Zen, as he handles his rejection by Takano.
Zen Kirishima (桐嶋禅 Kirishima Zen?)
Zen Kirishima was first introduced in Junjou Romantica as the editor-in-chief of Japun, the shōnen manga magazine; here, he is now the new love interest for Yokozawa. He is raising his daughter, Hiyori, on his own due to his wife's passing a few years ago. After blackmailing Yokozawa, the two begin dating upon realizing their feelings for one another. He has a habit of teasing Yokozawa, calling him the "mother" of his daughter Hiyori.