In the Emerald Editing Department of Marukawa Bookstore, Ritsu Onodera works as a shoujo manga editor under his boss and also his "first love," the editor-in-chief Masamune Takano. While struggling to work as the production assistant for a new magazine while resisting Takano's authority, Onodera unexpectedly encounters Takano's friend, the sales department employee Takafumi Yokozawa...!?

Onodera reflects upon how he imagined Christmas would be when he and Takano were together 10 years ago. Onodera runs a manuscript over to the printers and upon arriving back at the office, he receives an email from Takano telling him he can go home. As the elevator door opens, he sees Takano and Yokozawa talking and when the leave together, Yokozawa asks what Onodera’s plans are for the 24th, which happens to be Takano’s birthday. Yokozawa then implies to Onodera that he and Takano are still together, and he warns Onodera again to stay away from Takano. Onodera wishes Takano a happy birthday and as they part, Takano requests Onodera’s company on a drive for his birthday gift. On the drive, Onodera reflects on his feelings toward Takano, and Takano reveals the true nature of his relationship with Yokozawa and reminds Onodera that he has loved him for 10 years. They kiss, and Onodera admits to himself that he cannot resist Takano.

The triangle between Yoshino, Tori, and Yuu is coming to the tipping point. Who will be the first to speak their heart? Source: crunchyroll

Chiaki Yoshino, a highly successful young female manga artist who had just finished a big project, made plans to go out with her childhood friend and editor, who also happened to be her boyfriend, Yoshinori Hatori. However, on the day of their outing, Hatori had to cancel due to a sudden work emergency. Yoshino reluctantly decided to go out alone, but while wandering around the city, she coincidentally saw Hatori with another woman...!?

The Marukawa Bookstore's Emerald Editing Department had entered the new year with a refreshed mindset, but they were as busy as ever. Amidst the hectic workload, a new editor, Ritsu Onodera, was struggling to get their assigned manga artist to agree to revisions to their draft. Just then, Onodera received a call on their cell phone from someone unexpected...?

Ryuichiro Isaka, an editor working at Marukawa Bookstore, a publishing company owned by his parents, is a spoiled rich kid who joined the company due to family expectations, despite his aspirations to become a writer. His senior colleague and caretaker, Kaoru Asahina, had been taken in by the Isaka family at a young age due to certain circumstances and has been by Ryuichiro's side ever since...? "Junjou Mistake" depicts the past and present of Ryuichiro Isaka, the executive director of Marukawa Bookstore, and his capable secretary, Kaoru Asahina.

On the day of the annual New Year's party, where authors and other industry personnel are invited, Ritsu receives a phone call from his mother ordering him to pick up his childhood friend, An from work. Furthermore, while attending the party for the first time and being introduced to a writer by Takano, Ritsu unexpectedly runs into Yokozawa, who had come as a representative of the sales department...!?

Shota Kisa, an editor at Marukawa Bookstore's Emerald Editing Department, is in a relationship with a younger art school student named Kou Yukina. Despite being happy with Yukina, Kisa feels anxious that Yukina never voices any complaints about Kisa prioritizing work over their relationship. Finally realizing that things cannot continue as they are, Kisa makes a promise to finally make time to meet with Yukina...?

After seeing something shocking at Snow's part-time job, Kisa was unable to focus on his work from that day on. Before getting hurt by being told to break up, Kisa decided to disappear from Snow's life by fading away their relationship. However, at that time, Snow called Kisa and said, "I want to meet you" over the phone...

"Do you really like me 10 years ago?" - Utterly shaken by the sudden words from Takano, Ritsu is unsure whether to confess her feelings to him before regretting it. One day, Takano catches a cold and takes a day off work, and Ritsu wonders if she should check on him and maybe finally reveal her true feelings.

Takano and Onodera share a moment in the rain and talk about their time in school. A few startling truths are revealed that may change their opinion about each other.

On the way to work, a memory from the past suddenly came back to Takano, which was the incident that became the starting point for his interactions with Ritsu. In high school, Takano used to spend his afternoons in the library. He noticed the presence of someone who always borrowed the same books as him and watched him from a distance, but...? A first love story is told from Takano's perspective!