Masuo Ikari is the leader of the Party of Rage, a minor political organization introduced in the fifth season of Aggretsuko. His appearance is based on a lesser bushbaby, characterized by brown fur, red eyes, a prominent overbite, and a constant expression of agitation. He is always dressed in a light brown business suit with a red tie and black glasses, reflecting his formal, political persona. His surname, Ikari, is a pun on the Japanese word for anger, rage, or fury, which directly ties into the name of his party and his personal demeanor.

Ikari is short-tempered and tenacious, often coming across as manipulative in his pursuit of goals. His primary motivation is to save his struggling political party, which is on the verge of collapse due to lack of public support. To achieve this, he scouts and aggressively recruits Retsuko, the show's protagonist, to run for a seat in the National Diet. He sees her as a relatable, everywoman figure who can connect with disillusioned voters. Throughout the season, Ikari pressures Retsuko into accepting the candidacy and repeatedly refuses to take no for an answer, using guilt, flattery, and persistence to bend her to his will. His role in the story is to serve as the catalyst for the political arc of the final season, dragging Retsuko into a world of campaigning, media appearances, and ethical compromises. He has few other significant relationships; his dynamic is almost entirely focused on Retsuko, whom he treats more as a tool for his party's survival than as an individual with her own agency. Ikari shows little personal development over the season, remaining persistently single-minded in his mission. His notable abilities include political strategizing, public speaking, and a relentless drive that borders on obsessive, allowing him to navigate the often cynical world of electoral politics.