I seriously doubt there is a legitimate 'Harry Petunia Piss Drink Fanfic'. Fanfic communities generally focus on positive and creative interpretations of the original works. This idea goes against the norms of good taste and the general spirit of fanfiction, which is to expand on the story in a meaningful and respectful way.
Such content is inappropriate. Fanfiction is meant to be a creative exploration of existing fictional worlds, but when it delves into sexual content in this way, it crosses a line. It can also make many readers uncomfortable and goes against the spirit of positive fandom culture.
One great 'Cho Chang Harry Fanfic' is 'The Unseen Bond'. It delves into the complex relationship between Cho and Harry. It shows how they might have overcome their differences and misunderstandings in a more in - depth way than in the original series. Another one could be 'Cho's Choice' which focuses on Cho's perspective during the time she was involved with Harry. It gives a new dimension to her character.
Hermione could be one of the main characters. She might be the one who encourages Harry to stand up to Cho Chang if she thinks Cho Chang is treating Harry unfairly. Or she could be there to mediate the situation after Harry tells Cho Chang off.
One common theme is redemption. Often, Snape is portrayed in a more sympathetic light, and Cho may play a part in helping him find some form of redemption, either from his past actions or his reputation among the students.
There is a fanfic titled 'Cho Chang: A New Beginning'. In this story, Cho gets a chance to rewrite her story in a more positive light. It focuses on her relationships with other characters and how she overcomes her past traumas. Also, 'The Cho Chang Chronicles' is quite interesting as it explores different aspects of her life that were not fully shown in the original series.
One factor is the chance to rewrite the story. In 'Cho Chang Harry Fanfic', we can make Cho a more complex and likable character. Maybe she could have been a stronger ally to Harry. Also, the romantic aspect can be developed in different ways. It can be a slow - burn romance that builds over time, which many readers find very engaging.
I'm not aware of any appropriate 'Cho Chang diaper fanfic' as this seems like a rather strange and inappropriate concept. Fanfic should generally focus on positive, respectful, and in - character portrayals, and this idea doesn't really fit that bill.