We did wild mass guessing back at SP?
Anyway, it's in the wiki under Takagi's trivia that Takagi does (at least, in iM@S1) brag about the idol he produced falling in love with him, and under Kotori's trivia that she and Takagi are very close, and that Kotori used to be an idol... Maybe I came to that conclusion on my own, somehow? :s I'll ask someone who knows a bit more about Kotori than I do next time I get the chance.
Also, that probably didn't need to be under spoiler warning, but better safe than sorry.
Also also, this post is officially off-topic. Sorry 'bout that.