Some Sample Prompts...
Harry, age 25 or so, finds himself actually writing fan mail to a newish author of science-fictiony romance novels. Really steamy ones. The author never writes back, which, not that Harry wants to bank on his name, but seriously, no one in the wizarding world doesn't write back to him, and it's a wizarding publisher. So, Harry goes looking for her. Who knew Snape would take up a second career writing smut?
When helping Lily learn her lines as Maid Marian/Guinevere/Little Orphan Annie/etc. for a Hogwarts production of Robin Hood/King Arthur/Annie/etc., Harry is zapped by a random hormonally-induced teenage spell-gone-wrong. Now he thinks he's the hero (of whatever production you choose) and Severus Snape is the heroine (of said production), whom he's determined to rescue from A Cruel Fate. (Could be artwork or a story.) Bonus points if Harry thinks the people around him are other good/evil/indifferent characters (in whatever story the production is about).
Seamus Finnegan decides that the wizarding world needs a decent brewery, so he becomes an entrepreneur set to take the magical pub world by storm. He holds a "Best Brew" recipe contest as a publicity stunt, and Ron and George Weasley decide to enter their family's secret home brew, the "Lusty Love Lager", which they swear leads to true love and is the secret of the Weasley family's phenomenal marriage and baby-producing track record. The contest comes down to several brews, including the Weasley beer and one from a mysterious masked brewer. Harry's a high profile guest judge on the day of the event. Is it just a buzz brought on by sampling unusual magical beers, or does that mysterious masked brewer bear an uncanny resemblance to Severus Snape? And what the hell?! Did Ginny really use the potent home brew to get Harry drunk enough to propose to her?
This is rarely an issue, because not that many people share compatible patronus creatures, but it turns out if your patroni mate, it can lead to some surprising consequences. Harry didn't even know pregnancy was possible for wizards.
Severus and Harry had been together for a few months after Harry graduated before Harry, because of his superficial youth, left Snape to 'enjoy his life'. Now, a few years later, Harry truly understands what he has lost. He decided to win Severus over again. But how can he do that when Severus treats him like nothing, and a certain Malfoy is his competitor?
When little Lily eagerly promised her friend Severus that she would marry him and love him forever, little did she know that magic heard her words and felt the truth ringing in them at the time. So the magic took and ran through Lily's blood. When Lily didn't fulfill her promise before her death, the magic dormant in the only blood that remembered that promise started to stir; and once the seal that Voldemort's brand on Harry was removed nothing stood in its way any longer.
Snape teaches his godson, Scorpius, how to woo a Potter by practicing on Harry. Prefer Albus Severus for Scorpius.
AU. After several years abroad, 40-something Severus Snape comes home, ready to settle down. Lily and James Potter help their good friend to find a suitable spouse by arranging a string of dinners/dates/parties in their home. What happens when Harry starts noticing Severus (or vice versa)?