This was too cute! I love a clueless Derek, so worried that the happiness he's finally found won't last forever, and figuring out maybe it can.
In this one, Derek doesn't know what to get for Stiles. He bumbles around a bit, buying random mall stuff, and finally decides to fuck Stiles, something he hasn't done since their first time, which was a "sex pollen" thing (and if that story exists, someone please tell me, I wanna read it!
So it turns into a really cute, really HOT gesture on Derek's part, making this just an adorable little story.