This inspired by the scene in Batman: Under the Red Hood except this takes in the Miraculous Ladybug universe in which Nathanael confronts Batman after being brutally beaten at the hands of the Joker.
Batman/DC Comics
Miraculous: Tales of Ladybug and Chat Noir/Zagtoon
Nathanael pointed the pistol at Batman as he stood up. "Is that what you think this is about? That you couldn't save me?" Nathanael angrily asked. "I don't know what cloud your judgement worst. Your guilt or your antiquated sense of morality."
However Batman only stood silently as Nathanael continued. "Batman, I forgive you. For trying to save me. But why? Why on god's earth..."
Nathanael kicked down the wooden door revealing the Joker tied to a chair. "Is he still alive?!"
The Joker then laughed despite being in his tied up state, he still manages to get a good laugh as if he is having a good time. "Got to give the boy points. He came all the way back on his own two feet to make this shindig happen. Who's got a camera? Oh, I know. Get one of me and the boy first. Then you and me, then with buggirl and catboy, then all of us, and then one with the crowbar, then..."
Nathanael kicked the Joker to the ground sending him sliding across the room. He then kneel down to point the gun at Joker's at head before saying, "You say another word and I'll put one in your lap first." Only for Joker to reply, "Party pooper. No cake for you."
"Ignoring what he has done in the past. Blindly, stupidly disregarding the entire graveyards he's filled, the thousands who have suffered, the friends he's crippled!" Nathanael added. "And I thought... I thought I would be the last person you'd ever let him hurt. If it had been you or Ladybug he had beaten to a bloody pulp, if he had taken anybody from this world, I would've done nothing but search the planet for this pathetic pile of evil death worshiping garbage! And send him off to hell!"
"You don't understand, Nathan. I don't think you ever understood." Batman finally replied. "Understand what? That killing would be against your nature? Because Batman would never kill. Even a sadistic, murder loving psychopath?" Nathanael retorted back.
"No! God almighty! No! It would be too damned easy." Batman answered. Ladybug and Chat Noir stared wide eyed and shocked at what Batman said before he continued. "All I ever wanted to do is kill him. A day doesn't go by when I think about subjecting him to every horrendous, mind-boggling forms of torture imaginable. All of it building to a point leaving him begging. Screaming for mercy in the worst kind of agony imaginable."
The Joker looked at Batman with a still present smile on his face. "Aw, so you do think about me." Batman continued, "I want him dead. Maybe more than anything I could've ever want. But if I do that, if I allow myself to go down into that place, I'll never come back."
The entire room became filled with silence as they have just witnessed the unheard of side of Batman. Batman as someone known for having a sharp mind and serious demeanor, also harbors a deep urge to kill the Joker. "That it? That's your answer?"
Nathanael broke the silence. "I don't think you understand. I'm not talking about killing Scarecrow, Riddler, Hawkmoth, or anybody else! I'm talking about him! Just him! I'm doing this because... because he hurt me."
Batman only replied, "I can't. I'm sorry. I just can't."