Character growth is an important characteristic. For the reader - insert, they could start off as a novice ninja and grow in strength and wisdom with Madara's influence. For Madara, the fanfic could show a different side of him, perhaps a more vulnerable or compassionate side when interacting with the reader. The setting should be well - described too, whether it's the Hidden Leaf Village or some other location in the Naruto world. And the dialogue should be natural, reflecting the personalities of both Madara and the reader, making the interactions between them feel real and engaging.
In a great 'madara x reader' fanfic, the relationship between Madara and the reader is key. It should be believable and gradually developed. If it's a romantic relationship, there should be moments of chemistry and mutual understanding. Also, the writing style matters. A vivid and descriptive style can really bring the story to life, making you feel like you're right there in the Naruto universe with them. It might also include accurate references to the Naruto lore, which adds depth to the fanfic.