Well, 'oh hell no' is an expression of strong disapproval or refusal. In the context of 'Harry Potter fanfic', it might mean that someone really doesn't like a particular Harry Potter fan - created fictional work. Maybe they find the plot too outlandish, or it goes against their idea of the original Harry Potter universe.
Well, it could also be that the creation process of this fan fiction has been a hellish experience for the writer. Maybe they faced a lot of difficulties like writer's block, negative feedback from other fans, or problems with staying true to the original source material while trying to be creative, and all these issues have manifested in the final product as a 'hell - like' fan fiction.
Typically, megumi fanfic often focuses on his personality traits. His stoicism and determination are often highlighted. For example, in many fanfics, his unwavering resolve in the face of danger is a central theme.
Well, Megumi's story in the manga was full of twists and turns. She had to overcome various obstacles, and there were also some unexpected developments in her relationships with other characters.
The characters need to be relatable again. If they've been distorted, go back to their original traits and build from there. Add more depth to them by giving them proper motives and emotions. Also, consider the overall tone. If it's too dark, adding some lighter moments or a glimmer of hope can improve it a great deal. It doesn't have to be all doom and gloom. And finally, get some feedback from other fans or even non - fans who can give an objective view on what needs to change.
Someone might say it if the fanfic contains really bad writing. Like if the grammar and spelling are atrocious, it can be a turn - off. Also, if the story is just plain boring or the characters are not well - developed.
As of the latest chapters I've read, Megumi is still alive in the manga. Usually, such major character deaths are significant plot points and would be well-publicized if they occurred.