So, a brief summary:
It's valentines, and main girl Yuuha-chan made cookies to give to the boy from the other class, Kawanishi-kun. They're honmei (love) and it's implied these two are dating.
Then, she's called to the soccer club storage room by Sensei, because she's the club manager and he's the club adviser, and the room needs organizing.
She uses this opportunity to give him chocolates too (giri, or obligatory).
He also says he won't be around next year, because he'll be teaching at another school.
The mood develops a bit and they have an exchange kinda like this:

Yuuha: "We can't ..."
Sensei: "Your excited face tells me otherwise"
Yuuha: "That's why we can't ..."
Yuuha: (Sensei has such an adult scent, I like it)

Then they have sex.

Base +8, Eighties Grind +5, Aiveil +7