Mitsuru Kirita serves as Vicecommander of the Gaia Fleet, Earth's primary defense force, under Commander Tôdô. He is driven by strict adherence to protocol and harbors a deep-seated hatred for Captain Harlock, whom he initially condemns as a coward and outlaw, believing Harlock's methods undermine lawful authority and Earth's established order.

Kirita's rigid personality stems from personal tragedy. During his youth, his father, a government agent, perished on a mission. This loss was followed by the deaths of his mother and younger sister, Tami, profoundly shaping his worldview and fueling his dedication to protecting Earth through institutional means.

As the Mazon threat escalates, Kirita champions planetary defense within Earth's leadership, standing in stark contrast to the apathetic Prime Minister. Despite his hostility toward Harlock, he is one of the few willful figures prioritizing Earth's safety over comfort or political maneuvering. His operational focus remains mobilizing the Gaia Fleet against external threats, even as he opposes Harlock's independent actions.

A critical shift occurs when Kirita confronts the scale of the Mazon threat and witnesses Harlock's unwavering defense of humanity. This forces him to reassess his rigid beliefs. He gradually acknowledges his ideals align with Harlock's goal of protecting Earth, leading to a strategic realignment. Ultimately, Kirita sets aside his enmity, cooperating with Harlock to confront their common enemy, evolving from antagonist to ally.