I read it a while back so I don't remember much about. I do remember that the main characters were the Prince (King?) of Darkness who fell in love with the Prince of Rainbows (called Rain). Anyway, Rain ended up getting kidnapped and the Prince/King went searching for him.

I think the series started with the letter "A" but it could be something else. I honestly can't remember.

That's Neo Arcadia.

Thank you!