Hi! I'm afraid I'm a little fuzzy on the details as I read this a long time ago, but I'm itching to find it again. The few details I definitely remember are

• Sam and Dean are both werewolves;


• Sam claims Dean against a tree;


• Heavy mentions on the incest bit, how having offspring between two siblings somehow made the child stronger because of werewolf biology (or something like that), with Sam insisting on knocking Dean up;


• Dub-connish

If anyone has any ideas on what this story might be, I'd greatly appreciate it! Thank you so much in advance!

P.S. I'm new to this community, so if I make any mistakes please tell me and I'll fix them right away. Thank you!

Found it, thanks to alexxkah! : 25th Summer, by sdwbf