Gintoki x Shinpachi Sensei x student Shinpachi has a crush on his sensei, Gintoki, so he goes to his place and cooks him dinner every day. With this, the sensei slowly falls for the charming student.
This is one of those fanworks that, with a bit of tweaking, would be a good standalone (original) work. The relationships would still be interesting to a reader who didn't know Gintama, etc.