I remember this 2chapter one shot was on Fakku a few years ago, by a prominent artist that had a similar style to Yuzuki N and Napata.

The plot: a boy goes back to his hometown for summer and first scene has him eating a popsicle talking about how boring it is and there's nothing to do, when a short-haired girl in a tracksuit and bike shorts interjects and says that's not true. they eventually walk around and end up by the riverside where they have sex.
After she goes back to school, the 2nd chapter has a time skip where the boy now attends the same school as the girl and they remember each other; and they also both are on the track team. She gives him a massage for his aching legs too.

What is this one-shot title, does anyone know?