You can start by looking on fanfiction websites such as Archive of Our Own (AO3). It has a large collection of Harry Potter fanfictions, and you can search for 'Draco Hermione Guilty Leash' in the search bar. There are likely to be some well - written stories there.
A possible plot could be that the 'guilty leash' is a symbol of Draco's debt to Hermione. Hermione, who has always been an advocate for justice, uses the leash to make Draco do good deeds in the wizarding community. As they work together on these projects, like helping out at Hogwarts or in the wizarding hospitals, Draco starts to see the world from Hermione's perspective and they develop feelings for each other along the way.
There could be a fanfiction where the clamp leash is an object in a magical game or tournament. Draco and Hermione are on opposing teams, and the leash has certain magical properties that affect the outcome of the game. This would create an interesting dynamic between them as they both try to outwit each other while also being connected by this strange object.
Well, it depends on the writer's creativity. It could be a tool for power play. For instance, if Draco is in a position of power, the clamp leash could be a symbol of his control over Hermione in a story set in a dark, alternate Hogwarts. But this is just one way to look at it.
One possible fanfiction could be about a magical creature Draco that is tamed and put on a leash by a powerful wizard. The wizard might be using Draco for some sort of mission, like exploring a dangerous enchanted forest. Draco could be a dragon - like creature with its own will, and throughout the story, it struggles against the leash both physically and emotionally as it tries to assert its independence.
Draco and a harness leash could be part of a story where he's in a magical circus. He's in charge of some magical animals and the harness leash is what keeps them in line. But Draco might start to have second thoughts about keeping these animals in captivity, and the harness leash becomes a symbol of his internal struggle between duty and compassion.
One possible fanfiction could be about Draco using a harness leash in a magical creature training scenario. Maybe he's trying to tame a rare and unruly beast, and the harness leash is a special magical tool. He has to use his Slytherin cunning to figure out how to work with the creature while using the leash effectively.
In 'leash on draco fanfiction', it could center around a power dynamic. Draco is often seen as a proud and somewhat haughty character. So having him on a leash could represent a shift in power. For example, another character might be in charge of him, and this could lead to all sorts of interesting interactions, like the character using the leash as a means to make Draco do things he wouldn't normally do, or it could be a part of a redemption arc where Draco has to submit to certain conditions to grow as a person in the fanfiction world.
One popular 'Draco and Hermione guilty' fanfiction is 'Guilty Pleasures' which delves deep into their complex relationship. It shows how they struggle with their feelings in a world where they are supposed to be on opposite sides. Another one could be 'The Guilty Secret' which focuses on a secret encounter between them that changes their dynamic forever. There are also some on platforms like FanFiction.net where you can search using these keywords to find more.
I'm not sure specifically which ones are the most popular, but there are likely some out there. Fanfiction websites are filled with all sorts of creative takes on characters, and a concept like 'leash on draco' is bound to attract some attention. You could start by looking on major Harry Potter fanfiction platforms and search for stories with that title or related tags.