I'm not entirely sure specifically about the 'Pretty Little Liars Original Sin Mouse Story'. It might be some sort of sub - plot within the 'Pretty Little Liars Original Sin' series that involves a mouse in some way, perhaps as a symbol or part of a mystery.
The main plot involves a group of girls being tormented by an unknown assailant, who seems to be out for revenge related to secrets from the past. There are mysteries surrounding their parents' past actions that are starting to resurface and impact the girls' present lives.
One common theme is secrecy. Just like in the original show, characters in the gay fanfiction might have to keep their relationships a secret due to the small - town environment or family expectations. Another theme could be self - discovery, as the characters figure out their sexual orientation in the midst of all the drama.
Love against all odds is also a big theme. They might face opposition from friends, family or the society within the PLL world. For example, they could be worried about how their friends in the clique would react. Another theme is self - discovery. The characters might be exploring their sexual identity while dealing with all the mysteries and chaos in Rosewood.
The original series was full of mystery, danger, and a lot of negative elements like blackmail and lies. In positive fanfiction, there's often more focus on the good in the characters. For example, instead of the Liars constantly being in fear of 'A', they are more focused on building their relationships and achieving their goals.
Well, Archive of Our Own (AO3) is a great place too. It has a large collection of 'Pretty Little Liars' fanfiction, including gay ones. You might find stories that pair up unexpected characters in a gay relationship, adding a new and interesting dynamic to the already complex world of 'Pretty Little Liars'. It's really fun to explore different takes on the characters' relationships in this way.
A common theme is also the coming - out stories of the characters. Writers might explore how a character in the Pretty Little Liars world comes to terms with their sexual orientation, dealing with the reactions of friends, family, and the secrets that come along with it. It adds a new layer of drama and character development to the existing storylines.
Another option could be Tumblr. There are often fanfic writers who post snippets or links to their Pretty Little Liars gay fanfics on their blogs. You can search for relevant tags such as '#PrettyLittleLiarsFanfic' and '#GayFanfic' to find what you're looking for.