Sekai-ichi Hatsukoi: The Case of Ritsu Onodera 6 (世界一初恋 〜小野寺律の場合6〜, Sekai-ichi Hatsukoi ~Onodera Ritsu no Baai 6~) is the sixth volume of the Sekai-ichi Hatsukoi manga series.
- The Case of Ritsu Onodera No.10
- The Case of Masamune Takano No.1
- The Case of Ritsu Onodera No.11
- The Case of Masamune Takano No.1.5
In "The Case of Ritsu Onodera No.10," the confrontation in the previous chapter still hangs over Ritsu Onodera, Masamune Takano, and Takafumi Yokozawa. Back at work after his illness, Takano confronts Yokozawa and makes it clear that he loves Ritsu. Yokozawa accepts this and returns to sales, where a coworker says that Ritsu's project proposal is basically perfect, which pisses Yokozawa off more. Ritsu gets caught in the rain and runs into Takano, who followed him out. They talk about things and Ritsu confesses, but his words are drowned in a burst of rain. They go back to Takano's apartment and have sex. The next day at work, Ritsu has caught Takano's cold. He runs into Yokozawa and they establish that they'll still be professional together. Takano arrives and he reject's Saitou's storyboard, so Ritsu has to tell her to start over completely.
"The Case of Masamune Takano No.1" is the first chapter told from Masamune Takano's perspective. Takano falls asleep on the train to work, and reflects on how Ritsu currently is and how he used to be in high school. He figured out who Ritsu is by seeing his name on all the books he checked out. They go out to eat, and Ritsu gets extremely anxious just from ordering food, but they talk and Takano finds himself enjoying talking about their shared interests in the stories they read. Takano is also dealing with the turbulent separation of his parents, and the anger builds until he explodes at Ritsu, but Ritsu later returns and apologizes. When Takano tries to hold his hand, Ritsu panics and runs home. A classmate later confesses to him, but Takano turns her down, slowly realizing that he's fallen in love with Ritsu. Back in the present, Ritsu wakes him up because their stop is coming up. Takano is still ill, and after exiting the train he sits on a bench. He holds Ritsu's hand saying that he needs an energy boost, which Ritsu allows.
In "The Case of Ritsu Onodera No.11," Ritsu and Takano go on an overnight business trip together. Ritsu is taking on managing a third mangaka, Kaitou, and he and Takano take a train to meet her and discuss the handover. It's the last day of a festival there, and when work finishes, Takano and Ritsu watch some of the fireworks. There's a mixup with their hotel booking and they end up sharing a room with a single bed. They talk about getting to know each other better and what to discuss other than work, and they end up having sex. The next day after taking the train back, an employee from general affairs apologizes for the mixup with the hotel booking and Takano tells everyone in the department that they ended up having to share a room. Shouta Kisa teases Ritsu for details about what happened and Yoshiyuki Hatori calls Chiharu Yoshikawa to share the story to help with writers block, to Ritsu's horror.
"The Case of Masamune Takano No.1.5" is a three-page flashback chapter from Takano/Saga's perspective during high-school. He and Ritsu are walking to his place after Saga invited him over. Saga wonders what they should talk about, since they already talked about the books they both like, and Ritsu is walking very stiffly. Saga isn't sure where to start a conversation, but he finally tells Ritsu he doesn't need to be so nervous.
- Kazuma Henmi, Yokozawa's coworker
- Nanako Saitou (referenced), Takano rejects her storyboard
- Takano's female classmate who asks to borrow his notes and later confesses her feelings to him
- Takano's father, a surgeon
- Kotoko Saga, Takano's mother, a lawyer
- Sano, Takano's guidance councilor who holds an interview for his university choices
- Akihiko Usami (referenced only), an author publishing in Shosetsu Koharo magazine which Takano and Ritsu are both reading
- Kaitou, a mangaka who was previously managed by Takano and is now managed by Ritsu