"Sekaiichi Hatsukoi: Propose-hen" is a continuation of the "Sekaiichi Hatsukoi" series, focusing on the romantic relationships within the editorial department of the manga publishing company Marukawa Shoten. The story primarily centers on Ritsu Onodera, a former literary editor who transitions to the shojo manga department, and his complex relationship with his demanding yet charismatic boss, Masamune Takano. Their dynamic is marked by unresolved feelings from their high school days, when they were briefly involved in a romantic relationship under different identities. Takano, recognizing Ritsu despite his attempts to hide his past, is determined to rekindle their connection, while Ritsu struggles with his lingering emotions and professional boundaries.

The series also explores the relationships of other couples within the workplace. Yoshiyuki Hatori, the calm and collected editor-in-chief, navigates his relationship with the cheerful and sometimes naive manga artist Chiaki Yoshino. Their bond is tested by misunderstandings and external pressures, particularly from Yoshino’s family, who are unaware of his relationship with Hatori. Meanwhile, the playful and flirtatious editor Yuu Yanase finds himself drawn to the reserved and serious manga artist Kisa Shouta. Their relationship evolves as they confront their insecurities and past traumas, gradually building trust and intimacy.

The narrative delves into themes of love, identity, and the challenges of maintaining relationships in a professional environment. Each couple faces unique obstacles, from societal expectations to personal insecurities, but their stories are interconnected through their shared workplace and mutual support. The series balances lighthearted moments with emotional depth, portraying the characters’ growth as they navigate their feelings and commitments. The setting of a manga publishing company provides a backdrop that highlights the creative and collaborative nature of their work, further enriching the interpersonal dynamics. Overall, "Sekaiichi Hatsukoi: Propose-hen" continues to explore the complexities of love and relationships with a focus on character development and emotional authenticity.