>>48843586Lugia isn't a sea guardian. It roosted on the Brass Tower until it accidentally created a storm that destroyed the tower and killed the three nameless Pokémon inside. Out of guilt, it then exiled itself to the bottom of the Whirl Islands, where it would be unable to harm anyone again.
Beyond that, Ho-oh and Lugia are symbolic representations of the concepts of death and rebirth, a common dualistic theme to eastern religions (like Shinto, fitting for the Johto region).
