I'm not sure of specific fanfictions on this topic. You can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own. Just use the keywords 'lily sister marries severus' in their search bars, and you may find some interesting stories.
One possible plotline could be that the sister of Lily, initially having some sort of enmity or misunderstanding with Severus, gradually discovers his true self and falls in love. Another could be a more arranged - marriage - type situation where for some reason, they are forced to marry and then develop feelings over time.
One popular Severus Lily fanfiction is 'All The Young Dudes'. It delves deep into their relationship, exploring the complex emotions between Severus and Lily. It shows how their friendship evolved over time and how Severus's love for Lily was both a strength and a source of his pain.
One popular lily and severus lemon fanfiction is 'The Forbidden Love'. It delves deep into their complex relationship, exploring the unspoken desires between them. The story is well - written, with vivid descriptions of their emotions.
Well, I've read a fanfiction named 'Lily and Severus: The Forgotten Love'. It presents a unique take on their relationship. It begins with Lily finding an old diary of Severus which contains his deepest thoughts and feelings for her. As she reads through it, she starts to question her own feelings towards him. This story is full of emotional turmoil and self - discovery for both characters. There are also other great ones out there, but these are some of the ones that stand out in the 'lily falls in love with severus' genre of fanfiction.
One popular Severus Lily Lemon fanfic is 'The Lost Memories'. It delves deep into the complex relationship between Severus and Lily, with a touch of the 'lemon' aspect adding some spice. It's really well - written, with vivid descriptions of their emotions.
There's a fanfiction called 'Snape and Lily: The Untold Story'. It gives a lot of backstory to their relationship that was not fully explored in the original books. It shows how they first met, their early interactions, and how Snape's feelings for her began. 'In the Shadow of Lily's Love' is another good one. It focuses on Snape's life in the shadow of his love for Lily, how he feels like he can never be good enough for her, and how this feeling affects his actions. 'Lily's Love: Snape's Salvation' is also worth reading as it explores how Snape's love for Lily could potentially be his salvation from his dark path.
One possible plot could be that through some magical time - traveling anomaly, Harry ends up in a different time where he meets Lily before she is with James. They might bond over shared values and a sense of adventure, leading to their marriage. Another plot could involve an alternate universe where the normal relationships are disrupted, and Harry and Lily are brought together by fate to face a great evil together, and in the process, fall in love and marry.
I'm sorry, I don't have a specific fanfiction to recommend for this plot right now. But you can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own. Just use the keywords 'Harry Potter', 'aunt', 'Severus' and'marries' in the search bar, and you should be able to find some relevant stories.
Another theme is redemption. Severus is often seen as a character who is trying to redeem himself through his love for Lily. His actions, whether good or bad, are sometimes motivated by his love for her and his desire to make up for past mistakes.
There's also 'Lily's Perspective'. This fanfiction focuses on Lily's view of Severus. It shows how she might have truly felt about him, beyond just the friendship they had as children. It's interesting as it gives new insights into her character and how she might have dealt with Severus's darker tendencies while still holding onto the good in him.