"Koe de Oshigoto!" centers around Kanna Aoyagi, a 16-year-old high school girl who is unexpectedly recruited by her older sister, Miu Aoyagi, to work as a voice actress for an adult video game. Miu, the president of a company specializing in eroge (erotic games), pressures Kanna into taking the role despite her initial reluctance and lack of experience. Kanna’s shy and reserved personality makes the job particularly challenging, as she struggles to deliver the required lines with the appropriate tone and emotion.

The narrative explores Kanna’s journey as she navigates the unfamiliar and often uncomfortable world of voice acting for adult content. Her interactions with her colleagues, including the experienced voice actress Shino Ameku, provide both comedic and heartfelt moments. Shino becomes a mentor figure, guiding Kanna through the technical and emotional aspects of the job while also offering insights into the industry. Kanna’s growth is gradual, as she learns to overcome her insecurities and develop her skills, though her naivety and embarrassment frequently lead to humorous situations.

The series balances lighthearted comedy with moments of introspection, highlighting the challenges of stepping into a professional environment that clashes with personal boundaries. Kanna’s relationship with her sister is a recurring theme, as Miu’s overbearing yet supportive nature creates tension but also drives Kanna’s development. The workplace dynamics, combined with Kanna’s internal struggles, form the core of the story, offering a mix of humor, awkwardness, and personal growth within the niche setting of adult game production.