When writing this type of fanfiction, think about the backstory. What has led up to this moment where Batman hurts Nightwing? It could be years of pent - up frustration between them. Develop the setting well, whether it's the dark alleys of Gotham or the Batcave. Show the contrast between the two characters. Batman is all about justice at any cost, while Nightwing values relationships more. Let the story unfold gradually. Have Nightwing question his loyalty to Batman, and then have Batman come to his senses and try to make amends. This way, you can create a compelling 'Batman Hurt Nightwing' fanfiction.