Watanabe is a non-human companion from the same extraterrestrial origin as Yamazaki, sporting a dog-like form marked by distinct unconventional characteristics. He remains constantly by Yamazaki's side, serving as a dedicated attendant throughout their activities on Earth. Watanabe's unwavering loyalty drives his active participation in Yamazaki's schemes to achieve dominance within their classroom. He executes plans designed to influence classmates and undermine Tatsuya, the class representative seen as an obstacle. His presence significantly fuels the unpredictable and chaotic situations stemming from Yamazaki's leadership attempts. Watanabe also interacts with Yamazaki's human grandparents, who support the duo. Over time, their primary goal of planetary conquest fades, replaced entirely by the focus on establishing Yamazaki as the "King of the Class," with Watanabe instrumental in these efforts.

He leads a group called the "Watanabe Army" (Watanabe Gundan), associated with thematic songs performed within the series. Merchandise identifies him as a distinct character featured on collectible cards, specifically categorized as a "Prismatic Rare" item in the game's collection system.