@RobbyBevard:
She's got a successful career full of job offers that she keeps turning down in order to wait for Mashiro's dumb ass to get an anime. Hell, +Natural came and went as an anime already, and she could have been the starring lead in that.
And she's guaranteed the lead role in whatever our heroes come up with because… well, we've already seen that author request factors in when they got her the audio drama gig.... (which her manager noted was below her talent and pay level and not worth her time!)
She completed her goal. We can't ever see her anymore because that just stresses even further the fact that their promise is... dumb? And that Mashiro is holding back her career.
This would be the greatest plot twist ever, if Mashiro just called Azuki up and said:
"Hey, Azuki. Just noticing, you have pretty successful career as a voice actress, and I have a pretty successful career as a manga artist, and in retrospect that promise we made on a whim when we were 15 was pretty dumb. So you wanna get hitched?"
"Yeah, sure"