Responses
I definitely read that, I'll see if I can find it ;)
Free! dj - Sonogo no, Orera (Yaoi)
Maybe there was another one with a similar story but I can't find it.
You did it! That's the one. Thank you(โงโโฆ)
It's a fan-made doujinshi with characters from Free! Rin is the uke but i don't remember who the seme is.
they're a young and new couple that can't seem to have sex and their future selves come and teach them personnally