Kenji Yamazaki serves as a key blacksuit subordinate to Yukio Tonegawa within the Teiai Group's Team Tonegawa. At 30 years old, he leads the blacksuits and acts as a secondary authority on the team. His prior direct service under Chairman Kazutaka Hyōdō grants him unique insight into the chairman's habits and moods, making him a crucial resource for Tonegawa.

Initially skeptical of Tonegawa's leadership, perceiving it as self-serving, Yamazaki's perspective shifts during a company trip to Multitude House. Discovering rusty griddles meant for a team barbecue, he witnesses Tonegawa procure a replacement—unaware it is the Grilling Grovel punishment device. Tonegawa's gesture of sharing cooked beef solidifies Yamazaki's loyalty, transforming their relationship into one of mutual respect.

Yamazaki consistently demonstrates pragmatic judgment. He advises Tonegawa on Hyōdō's temperament, revealing that the chairman's post-bath mood can be read by the angle of his eyebrows—crucial for timing critical requests. During Tonegawa's illness, Yamazaki supports the reluctant substitute leader, Gonda, ensuring operations continue. His responsibilities extend beyond project management to overseeing Masayan's care staff, reflecting his trusted position.

In a pivotal moment, Yamazaki assumes temporary leadership of the Restricted Rock-Paper-Scissors game after Tonegawa loses his voice. Though fumbling the introduction, he adapts and successfully steers the event. His reliability contrasts with shortcomings of others like Ebitani's impulsiveness.

Years after Tonegawa departs Teiai, Yamazaki ascends to senior management. He mentors new blacksuits, upholding the disciplined standards instilled during his time under Tonegawa.