Am i blind or not?
I can't see the crush on who from who...
Just recently the crushes are blatant. But Aoba has had one on Kou since the start of the series. She just didn;t think kissing her ass was the way to win her love, she wants to imitate her success as boldly as Kou did. It's impossible because she's already much older than Kou was when Kou was way better than Aoba is now and playing in the big leagues (as a teen).
There is another girl there Hifumi that has some romance with Aoba, and Aoba and her best friend Nene are in one of those "no, I am the onee-san" contests that often lead to romance. Most people ship her with Hifumi, because Nene likes her former superior there.
The issue with Kou is that she has someone already who loves her completely, so she's a bad match for Aoba. (and usually her direct boss!). None of this is doujin or doujinshi, it's in the series. Just lately has the subtext become a little texty.