Shuudansha is a publishing company in the Sekai-ichi Hatsukoi series. It publishes Weekly Earth manga magazine, and Masamune Takano used to work there as an editor.
Takano used to work at Shuudansha as a manga editor, but he ended up leaving due to personal conflicts with Arata Haitani. Haitani holds a grudge against Takano, and he tries to hook up with Ritsu Onodera possibly just because he knows Takano likes him.
Saeki is currently a manga editor at Shuudansha. Before working there, she and Ritsu used to work together at Onodera Publishing. When they meet up again, they are both surprised to find that the other has moved from editing literature to editing manga. When they run into each other again, Saeki is with Arata Haitani, which is how Ritsu and Haitani first meet.
Weekly Earth (週刊アース, shuukan aasu) is a weekly shounen manga magazine published by Shuudansha. It's the main competitor of Marukawa Publishing's shounen magazine Japun.
- Shuudansha's real-world equivalent is the Japanese publishing company Shodensha.