Kōichi Yadoya is the president of ADventure, a small advertising agency in Tokyo where the protagonist, Akagi Madoka, begins working after moving from her hometown. He is portrayed as a middle-aged man with a warm and somewhat absent-minded demeanor, often forgetting important details or appointments in a way that resembles the Pokémon Slowbro, a creature known for its slow-wittedness. Despite his forgetfulness, he serves as the unifying figure of the office, gently steering his employees through their daily challenges without being overbearing. His role in the story is primarily that of a supportive boss who trusts his team and allows them room to grow, reflecting a laid-back management style that stands in contrast to the high-pressure creative industry around them.

Yadoya’s background is lightly sketched through his interactions: he is the founder or owner of the agency, and his long tenure has made him familiar with both the struggles and small victories of the advertising business. His motivations are not explicitly spelled out, but his actions suggest a genuine desire to see his employees succeed and to maintain a harmonious workplace, even when projects become stressful. Key relationships include his daily dealings with Madoka, the sales staff Hiyama and Kogusuri, designer Meguro, and the young trainee Koyama. He treats them all with a paternal patience, occasionally offering advice or encouragement, though he rarely takes center stage in major plot developments.

The character does not undergo a dramatic transformation over the course of the series; instead, his development is subtle, shown through moments where his forgetfulness leads to humorous or mildly inconvenient situations that the staff must work around. His notable trait is this forgetfulness, which is both a comic element and a reflection of his easygoing nature. He has no special abilities or skills emphasized beyond his role as a manager, and his presence provides a stable, grounding anchor for the lively personalities in the agency.