Kou Seiya is the leader of the Sailor Starlights and the lead vocals for the Three Lights. In general, Seiya acts arrogant and tends to be, at least on the surface, confident in his/her own abilities.
Over the course of the series, Seiya develops strong feelings for Usagi and his attempts to forge a bond with her provides the primary romantic tension of the season. From their first meeting on, Seiya calls Usagi odango, like Mamoru does. The two even go on a date at an amusement park, which prematurely ends when Sailor Iron Mouse attacks.
The relationship between Sailor Star Fighter and Princess Kakyuu is slightly ambiguous. In the manga, the princess had a lover who was killed by Galaxia. In the anime, it is implied Seiya’s romantic feelings for Usagi may be a confusion with similar feelings for Kakyuu.