You can try Fanfiction.net. It has a large collection of 'Draco and Hermione' fanfictions, and you can easily search for ones related to their bet. There are different categories and filters you can use to narrow down your search.
One great 'Draco and Hermione bet' fanfiction is 'The Betrothal Bargain'. It has an interesting plot where their bet leads to unexpected adventures and a growing understanding between them. Another one could be 'A Wager's Consequence' which delves deep into their relationship development as a result of the bet.
One popular theme could be the idea of redemption for Draco. In many fanfictions, he is shown to overcome his family's dark past and prejudice. Another theme might be the power of friendship or love that develops between Hermione and Draco, despite their initial differences. It could also explore how they navigate the complex wizarding world together, facing challenges from their respective houses and the general wizarding society.
In a fanfiction with this theme, it could be set post - war. Draco and Hermione find themselves in a situation where they are on the run from some dark wizards who are after them for different reasons. During their escape, Hermione gets wet and cold. Draco, having a change of heart after the war, gives her his warm cloak. This act of kindness begins to break down the barriers between them, and they start to have deeper conversations, realizing they have more in common than they thought.
Perhaps there's a fanfiction where a powerful and dark wizard from outside the school is targeting Muggle - borns. Hermione, being a Muggle - born, is understandably afraid. Draco, who has always had a complex relationship with Hermione, is conflicted. He doesn't want to see her hurt because, deep down, he has feelings for her. He ends up using his Slytherin cunning to outwit the dark wizard and keep Hermione safe.
One reason could be the traditional rivalry from the original series. In the books, they are from different houses, Slytherin and Gryffindor, which have a long - standing feud. Fanfiction writers might play on this by having Draco be mean as a continuation of that in - built tension. Another aspect could be his family upbringing. The Malfoy family has certain pure - blood supremacist views, and Hermione being a Muggle - born might be a target for Draco's meanness in fanfictions.
Another aspect could be that the leash situation is a way for the author to introduce some comical elements into the fanfiction. Hermione is known for her intelligence and seriousness, so seeing her in a situation where she has to abide by the rules of a lost bet and be on a 'leash' can create some really funny and unexpected scenarios. It can also show how she copes with being in a subservient position, which is very different from her usual role in the wizarding world.
She could stand up to him. Hermione is known for her intelligence and quick - wittedness. So she might use her sharp tongue and logical arguments to put Draco in his place. For example, she could expose his wrongdoings or the flaws in his pure - blood ideology.
One alternative theme could be a time - travel story where Hermione and Draco are sent back in time and have to work together to preserve the wizarding world's history. It's a fun way to explore their characters in a new setting.