"Deaimon: Recipe for Happiness" centers around Nagomu Irino, a young man who returns to his family’s traditional Japanese sweets shop, Ryokushou, in Kyoto after a decade-long absence. Initially leaving home to pursue a career in music, Nagomu’s return is met with mixed emotions, particularly from his estranged father, Kanou, who had hoped he would take over the family business. The shop, known for its wagashi (traditional confections), is a cornerstone of the local community, and its future becomes a central concern.

Upon his return, Nagomu discovers that Itsuka Yukihira, a young girl, has been living at the shop and is being groomed as the potential heir to Ryokushou. Itsuka, who was abandoned by her mother years earlier, has formed a close bond with Kanou and the shop’s employees. Her presence complicates Nagomu’s reintegration into the family business, as she views him with skepticism and resentment for his long absence. Despite this, Nagomu gradually begins to reconnect with his roots, learning the art of wagashi-making and striving to prove his commitment to both the shop and Itsuka.

The narrative explores themes of family, tradition, and personal growth as Nagomu navigates his responsibilities and relationships. His interactions with Itsuka, Kanou, and the shop’s loyal customers reveal the emotional and cultural significance of Ryokushou. The series also delves into the lives of the supporting characters, including the shop’s employees and the local community, highlighting their connections to the shop and its role in their lives.

As Nagomu works to rebuild trust and find his place within the family business, the story balances moments of humor, warmth, and introspection. The process of creating wagashi serves as a metaphor for the care and effort required to mend relationships and preserve traditions. Through its focus on the interplay between personal aspirations and familial duty, "Deaimon: Recipe for Happiness" presents a heartfelt exploration of identity, belonging, and the enduring value of heritage.