As an aside: this vending machine, man. It's like the vending machine at the crossroads of destiny. It's always the same one, in the same place, and when it isn't in the same place, it's because it's in Kou's mindspace.
I'm sure there's a pretty simple symbolism about it I have yet to think through, but I'm more humored by it as a recurring motif.
She was at least infatuated since about chapter 46, which reminds me about how she intended to have him fall for her.
But I ain't complaining, because this is older girl/younger guy at its best: old women being flustered as they fall below their originally presumed dignity as they get seduced by younger men armed with nothing but their earnestness and their will to mature.
You say that, and I'm not going to deny that there are editorial trends in these marketing demographics (and then there's josei, which is mostly smut), but there are plenty of seinen that would fit just fine in a shounen, and vice versa.
I would be as bold as to charge that the only essential difference between a shounen and a seinen is whether they can publish a nipple in the magazine.