Crossed The Line with my Rural Town Female Friend

Every year during summer vacation, Riku-kun heads to his grandfather's place in the countryside
There his female friend Nacchan comes over to say hi and play with him every year.
A year has passed since they last met, and Nacchan has become very attractive...
Nacchan doesn't act any differently, and she gets nice up and close with Riku-kun.
His heart is racing with excitement.
On the other hand, Nacchan is attracted to Riku-kun's new found manliness...
and eventually the two childhood friends cross the line and go all the way.