The return of the son of the relationship meme a la .hack//G.U. style! Comment here, listing your characters, and which of my characters they know. I'll reply with an affection~ meter~ to let you know what how they feel about you.
In terms of progression, it goes red --> blue --> yellow --> pink, with 1-5 dots signifying how close you are to moving to the next level. The base colour varies depending on the character. IT'S SUBJECTIVE and pretty. And if you get anything in the pink range, chances are, they either love you madly, consider you an incredibly important nakama, or want in your pants. Or all of the above!
Like she said, base color changes depending on the character. Maybe later I'll edit this with an explanation, but for example, with Shirley and Hyuuga it's basically impossible to get anything below blue, while every human starts at like Red +2 for Devit (Exorcists at Red +1).
I play Chisame Haru Viper Shirley Devit Hyuuga Rise