Chan, takes place during Harry's 3rd year: When Hermione tries to turn the hourglass on the timeturner, they're unexpectedly disturbed by a student barging into the infirmary. Hermione loses her grip on the time turner and by the time she and Harry finally catch it again, they're spinning back through time where they land in the entrance hall in front of seventh year student and loyal deatheater wannabe, Severus Snape. I think it'd be really neat if it would be avoided from turning into a dark!fic or rape/dubcon, but if you'd prefer to do that, it's fine.
Another chan: Snape is convinced Harry's the one who's been stealing from his stores, so he uses his unregistered animagus form to sneak into Gryffindor tower and snoop around bring the spoilt brat to justice. Unfortunately, he finds himself locked in the boys' dorm where Harry finds him and decides to take care of the obviously underfed and grouchy stray. While struggling with his situation, Snape sees a new side to Harry he'd never imagined.
After barely surviving Nagini's bite, Severus decides to live a quiet life. He moves out to the country after selling the house at Spinner's End, but instead of a peaceful retirement he finds Harry Potter on his doorstep. Harry's come to confess and insists that he loves Severus even though he's a virgin. Severus refuses to listen to Harry, after all he's always been straight, right? When Harry refuses to go away, Snape's dreams end up focusing on a green-eyed boy with a lightning bolt scar and a tight arse.
While teaching at Hogwarts, Severus is hit by a spell aimed at Harry. The spell causes Severus to lose all inhibitions and focus only on having his way with Harry.
Hermione and Ron manage to find Severus after years spent in hiding. Hermione pleads with Severus to return to the wizarding world -- Harry's under a sleeping spell and only true love's kiss can wake him. After Ginny failed, Hermione remembered Harry's obsession with the Prince and Snape and to Ron's horror comes to the conclusion that Snape is Harry's "prince".
After Ginny leaves Harry for someone else Harry's friends and family try to set him up with a new partner. Al discovers his father's secret stash of gay wizard porn (quidditch hunks edition!) and although Harry protests that it was just because he's a fan, the family decides to change tactics and begin setting Harry up with men, particularly quidditch players. However when the quidditch players prove to have roving eyes and Harry gets fed up with them, Severus Snape steps up to take Harry into hand, literally.