I really like the fanfiction 'In Moody's Shoes'. It takes the reader on a journey through Moody's eyes. You get to experience his paranoia, his skills as a wizard, and his complex relationship with the Order of the Phoenix. It adds a lot of depth to his character and is a great exploration for any 'Harry Potter' fan interested in Mad - Eye Moody.
The mystery surrounding Mad - Eye Moody makes fanfiction appealing. In the original series, he had a lot of secrets. Fanfiction allows us to explore those secrets further. For example, we can imagine what he was really thinking when he was teaching at Hogwarts.
One possible reason could be that he's worried about Ginny's safety during the pregnancy. He might be overprotective and his concern comes out as anger.
One of the most memorable is probably a wizard named Malachi in some fanfictions. He's mad because he was rejected by the Ministry of Magic for being too radical in his magic studies. So he goes on a rampage, using his unique and often dangerous spells against anyone who gets in his way. His character is really interesting because he has a complex backstory that makes you understand his madness a bit more.
It could be due to jealousy. Perhaps Ginny has been spending a lot of time with another character, and Harry misinterprets their relationship, leading to his anger. In fanfiction, the writers often play with such emotions to create drama.
There are those fanfictions where a mad wizard tries to create his own version of Hogwarts. He thinks the current Hogwarts is too 'goody - two - shoes' and wants to make a place where dark magic is taught freely. This kind of story usually has a lot of battles between the 'good' wizards and this mad wizard and his followers. It's full of action and drama.
One interesting fanfiction could be where Harry's anger at being entered in the Triwizard Tournament against his will leads him to discover a hidden plot much earlier. He might start to suspect that someone within Hogwarts is working against him and begins his own investigation. This could involve him using his skills in a more unorthodox way, like using the Marauder's Map to track the movements of the teachers and other suspicious characters.
I'm not sure specifically if there is a fanfiction titled exactly 'Harry is mad at Neville', but it's very possible. Fanfiction writers often play with different character dynamics. Neville is a character who has his own insecurities and growth throughout the series, and Harry also has his own emotional journey. A story where Harry is mad at Neville could explore their individual personalities and how they resolve their conflict.
Often, it starts with the initial moment of Harry getting mad. Then Ginny tries to figure out why he's so angry. For example, she might approach him and ask directly, but Harry could be too stubborn to tell her right away.