Long Live teh Snarry!
1. after HBP, Harry tracks Snape to a remote location, spies on him, and is eventually discovered via legilimency. struggle for dominance ensues. Who is whose prisoner? top!- or bottom!Snape, you choose.
2. Harry sleepwalking at Grimmald place, OOTP. Snape resists his persistent sleepy visitor, but not for long. Passion develops, and they must evade detection by Sirius et al. (Buckbeak knows how to keep a secret, but what about the house elves?)
3. Harry finds Severus living in (insert romantic non-anglo city) as a musician/composer. Piano, perhaps, or cello? He has built a wonderful life, but is deeply lonely (of course!) Enter Boy-who-Lived, freshly divorced and wandering in aimless melancholy. He is drawn to the music, but doesnt know why.