Episode 1 of "Uchi no Kaisha no Chiisai Senpai no Hanashi" begins with a sweet work relationship between Shinozaki Takuma, a younger employee, and his petite senior colleague, Katase Shiori. While Shinozaki is hardworking and respectful, Katase surprises with her efficiency by completing tasks swiftly. Outside the office, the two share a quirky moment when Katase gets distracted by a kitten in the bushes, highlighting her endearing personality.

Back in the office, their boss, Akina Chihiro, praises Katase for quickly submitting a project plan. The office atmosphere lightens further as Shinozaki and Katase laugh together about the struggles of desk work, leading to an amusing impromptu massage session between the two, where they take turns being the masseuse.

The episode also follows Shinozaki as he nervously prepares for a project presentation for a new employee. Fortunately, his reliable senpai, Katase, comes to his aid with a few comforting words and a small good-luck charm—a handwritten "Person" kanji.

The plot then shifts to a more social setting. Shinozaki, tasked with organizing a drinking party, tries to gather participants. A designer colleague, Yamagishi Aiko, readily agrees, while Hayakawa Chinatsu, another designer and Shinozaki's childhood friend, declines the invitation. Her refusal sparks a playful discussion about their friendship, causing some confusion in the office.

Finally, the episode concludes at a restaurant. Misunderstandings are cleared up when Katase expresses her desire to befriend Hayakawa, dispelling Shinozaki's thoughts about her jealousy. The episode ends on a high note as Katase shares a funny fact about her uncanny ability to attract cats.