Wataru Takagi is a dedicated detective in the Tokyo Metropolitan Police Department's Criminal Investigation Division 1. While initially showing some self-consciousness in his role, he exhibits consistent politeness and respect towards colleagues. His longstanding professional partnership with senior officer Miwako Sato deepens through shared high-stakes experiences, gradually evolving into mutual affection. During the Cherry Sapphire case depicted in the crossover film, Takagi operates under Inspector Juzo Megure. When Lupin III's activities, including an unusual diamond theft, draw police attention, Takagi volunteers alongside Sato to assist Interpol Inspector Koichi Zenigata, who specializes in pursuing Lupin. The investigation into the Cherry Sapphire gem theft leads to Lupin successfully impersonating Takagi. This disguise exploits Takagi's identity and position, allowing Lupin to bypass security and access the gem's secured location, facilitating its theft. In the line of duty during this case, Takagi wields standard police equipment, specifically a Nambu Model 60 revolver, during operations to secure the Toto bank vault. His actions contribute to the broader police response to the criminal events orchestrated by Lupin III, involving international figures and dangerous technology.