Seiya may be considered the nicest of the Three Lights. He lives with the rest
of them in an apartament and goes to the same high school the Inner Senshi go
to.
As Seiya, he is a popular pop singer. He is the lead voice (but is also responsible of the keyboard, writing lyrics and composing music) of the group and seems to be the most loose about achieving their mision. He is also member of the American Football Club. He is in love with Usagi, but of course she loves Mamoru (but yes, she likes Seiya). They end as friends, when he goes with his/her princess to start a new life, with his/her teammates.
Her/his name means Star Light. His/her powers are, as the rest of the Starlights, related to stars. The Sailor Starlights don't have any power-up. :P.