Ikkei Watanabe is a Japanese voice actor known for his long-standing association with the popular children's anime franchise Butt Detective (Oshiri Tantei). His involvement with the series began with its initial adaptation as a net anime in 2017, produced by Toei Animation. From the outset, Watanabe was cast in the dual roles of the series narrator and the character Chief Maltese, a role he has continued to reprise across various formats and productions.

As the Butt Detective franchise expanded from its original web short format to a regular television series on NHK's E Tele educational channel in 2018, Watanabe returned alongside the core cast to maintain continuity in his roles. His voice work as Chief Maltese has also been a consistent element in the franchise's feature film releases. He is credited in multiple theatrical installments, including Eiga Oshiri Tantei: Sufūre-to no Himitsu (Butt Detective: The Secret of Sufure Island) released in 2021, where his character's name is sometimes romanized as Chief Maltes. He also reprised the role for the 2024 film Eiga Oshiri Tantei Saraba Itoshiki Aibō (Oshiri) yo (Butt Detective: Farewell, Beloved Partner (Butt)), again providing the voice for Chief Maltese.

Watanabe's career is most prominently documented through his enduring participation in the Butt Detective series. His work demonstrates a long-term commitment to a single, major franchise, providing narrative guidance as the narrator and voicing the authoritative figure of Chief Maltese across its television series and multiple feature-length films.