Movie
Description
Kō Seiya is one of the three Sailor Starlights from the destroyed planet Kinmoku, and the civilian identity of Sailor Star Fighter. They arrive on Earth in search of their lost princess, Kakyuu, disguising themselves as the male idol group the Three Lights to conceal their true identities and to broadcast a telepathic signal through their music. Seiya enrolls at Juuban High School alongside Usagi Tsukino and quickly becomes the school's star athlete, excelling in American football and basketball, which creates a rivalry with Haruka Tenoh.

Personality-wise, Seiya is confident and often appears arrogant on the surface, but also reveals a passionate and occasionally impulsive or childish side, especially when showing off physical abilities. They act boldly without always considering consequences, particularly in matters of the heart. Seiya develops a strong romantic attraction to Usagi, addressing her with the nickname odango as Mamoru once did, and persistently pursues her despite Usagi's unwavering devotion to her missing boyfriend. This unrequited love forms a central emotional thread in their story. Seiya’s motivations are initially driven by the mission to find Princess Kakyuu and avenge their home world, but later expand to include a desire to protect Usagi and stand alongside the Earth's Sailor Guardians, even though the Starlights at first keep their distance from the affairs of Earth.

In the narrative of Pretty Guardian Sailor Moon Cosmos the Movie, the Starlights appear as mysterious figures who eventually reveal their true identities and ally with Sailor Moon to confront Sailor Galaxia and the Shadow Galactica. As Sailor Star Fighter, Seiya participates in several battles, notably defeating Sailor Animamates. The group travels to the Galaxy Cauldron, where Seiya and the other Starlights are killed by Sailors Phi and Chi and have their Sailor Crystals stolen, a pivotal loss that underscores the high stakes of the final conflict.

Key relationships include the deep, ambiguous bond with Princess Kakyuu, which carries hints of romantic devotion. Seiya's feelings for Usagi are openly expressed but not returned, leading to moments of poignant acceptance. Within the Starlights, Seiya is the leader and lead vocalist, with Taiki and Yaten often following but sometimes regarding Seiya as prone to childishness. The athletic rivalry with Haruka Tenoh stems from competition on the field and protective instincts regarding Usagi.

Development sees Seiya grow from a single-minded seeker of their princess into a warrior willing to sacrifice for a broader cause and for the people they have come to care about. Their final act is fighting alongside Usagi, accepting that their love will never be required but still choosing to protect her light.

As Sailor Star Fighter, Seiya uses the transformation phrase Fighter Star Power, Make Up to adopt a blue-and-navy Sailor uniform with high-heeled boots. Their primary attack is Star Serious Laser, which fires a powerful energy beam. Outside combat, Seiya is a talented musician who composes lyrics and plays guitar and keyboard for the Three Lights, and in civilian form demonstrates exceptional skill in American football and basketball.