Okay... When I was little, that was somewhere back at 90 or so when I was little, I saw this very nice cartoon (or maybe it was anime, I can't tell now). Now I'm trying to find ANYTHING about it. I doubt anybody will pay too much attention to my journal, but hell, hope dies last.
So, main hero is something in contact with stars/space/higher-forece. Wears something red-brown, has blond hair to shoulders and red band on his forehead. There's a triangle on his chest, I'm not sure was that something underneath his clothing or was it ON clothing.
He has friend, such pink little ghost/worm, that flies around him and never leaves him, very small little thing.
They travel around the world, seeking for crystals. Travel on flying machine made by that boy/guy. Crystals open doors/portals, but they are not the only ones who search for them... There's evil, which I can't remember
He loves/likes-a-lot this Siren/mermaid, blue hair, starfishes on her breasts, speaks little, but has very neat voice. Siren as siren should be.
She has her little friend - small purple/blue/violet starfish, that little wormy has an eye on her (starfish). She's smart and talks alot whenever met.

Now, what else... in one serie, Siren was kidnapped and that boy went to find her, in some... ice caves or underwater-something. I just remember everything breaking and he seeing her in some kinds of monitors.

In another serie, one of key-crystals is switched by that Evil into black one. It opens black-bad portal... I think they went into some pyramid or thing alike.

in very end, with titres going, that boy was showed in background of stars/space doing martial arts and acrobatic tricks.
At very last serie, he told his little worm friend "you have no idea what great power you have in you!" as he had to return somewhere where he belonged. Something tells me "stars son" but I'm not sure, it could've been only translation