He is the "leader" of the Three Lights (their band), but definitely not the leader of the Starlights. However, Seiya is the nicest and most romantic of the Three Lights. He is constantly flirtatious with Usagi, until they find out that she is Sailor Moon. Even then, however, it is still evident that he cares for her. There are times that he sees his Princess Kakyuu in her.

Haruka and Seiya don't like each other, and Sailor Star Fighter and Sailor Uranus don't like each other either. The dislike between Haruka and Seiya becomes strong when Haruka finds Seiya in Michiru's dressing room after a dual concert. The dislike between Sailor Star Fighter and Sailor Uranus exists because the Sailor Starlights are from outside of the galaxy, and therefore cannot be trusted. When they discover each other's true identities, the dislike becomes even stronger.

In my opinion, Seiya is the strongest of the Starlights. He is also the first of the Starlights to care about what happens to the Earth's senshi and the Earth. He is constantly helping them; he even saves Sailor Moon by jumping in front of Sailor Tin Nyanko's attack. This brave save causes the other two Starlights to become very angry with Sailor Moon, and yell at her about it being her fault that Seiya is injured. Later (I think that night), they are about to fight with the outer senshi on a rooftop. Seiya then appears and tells them not to fight. He says he won't see Sailor Moon, Usagi Tsukino, anymore. Poor Seiya and Usagi. :(

In the manga, the Starlights were actually girls dressing up like guys. In the anime, they are girls that changed their images to that of guys, until they transform. They are only on Earth to try to find their princess, Princess Kakyuu. They originally had absolutely no intent of protecting the planet.