"Inshokukei Onee-san ga Shitai Koto" centers on the interactions between a young man named Haruto and a series of older women who work in the food service industry. The narrative explores their relationships, which often blur the lines between professional and personal, as Haruto becomes a regular customer at their establishments. Each chapter typically focuses on a different woman, highlighting her personality, backstory, and the unique dynamics of her interactions with Haruto.

The women, often referred to as "onee-san" (a term denoting an older sister or mature woman), are portrayed with distinct traits and professions, ranging from a bar hostess to a café waitress. Their encounters with Haruto are characterized by a mix of flirtation, mentorship, and mutual support, often revolving around shared meals or drinks. The series emphasizes the warmth and comfort found in these casual yet intimate settings, with food and drink serving as a central motif that ties the characters together.

Haruto, the recurring male protagonist, is depicted as a somewhat reserved but observant individual who finds solace in the company of these women. His interactions with them are often lighthearted and playful, though they occasionally delve into more serious or emotional territory, revealing vulnerabilities and life experiences on both sides. The episodic structure allows for a variety of tones, from comedic and light-hearted to reflective and poignant.

The manga balances slice-of-life elements with romantic undertones, avoiding overt drama in favor of exploring the nuances of human connection. The focus remains on the characters' growth and the evolving nature of their relationships, with each encounter contributing to a broader tapestry of interconnected stories. The series captures the charm of everyday moments, celebrating the small yet meaningful interactions that define its narrative.