Disclaimer: never did and never will own it. Thomas Astruc does.
Spoilers: canon until Season 2, Episode 10 (Sapotis)
She pushed him in the room, the door slammed shut behind him and he sighed in relief. He turned around, grinning to her, but his smile disappeared almost immediately. He was alone. His transformation wore off in a green light, blinding him for a moment, but as soon as he opened his eyes again, this truth was still valid: she had sacrificed herself for him. He ran at the door, hitting it with his fists.
"Ladybug! Ladybug, no! Open this door!"
Unbeknownst to him, she had her forehead and hand pressed against the door.
"I'm sorry, Cat, I'm sorry. But I won't let you be hurt," she whispered.
"So this is the end."
She twirled around, on the defensive, but let down her guard as suddenly. It was useless anyway.
"You promised."
Hawk Moth nodded. "No harm to him and to those you care about. Though the list was quite extensive."
"No harm to anyone! If you have to take it on someone, let it be me."
Then a shout from the closed room behind her. "NO! Ladybug, no, don't trust him!"
"You understand the deal? I need a victim."
She nodded. "Yes."
"You know who I am?"
"Yes."
"Why do you do that?" he asked, genuinely curious now that he could see his goal.
"For him. So he will have a family and won't be alone anymore."
"Ladybug, no! I have you, now! You're my family!"
"It's not enough, kitty," she replied without taking her eyes from Hawk Moth. "I never was enough. Tikki, spots off."
Hawk Moth's eyes slightly widened when seeing her unmasked, but he didn't say anything. He pressed a button and a white smoke filled the room where Cat Noir – Adrien – was prisoner. A few moments later, Nathalie brought him the Cat Miraculous.
-o-o-
When Adrien recovered, he noticed instantly the absence of his ring. His shoulders slumped in defeat. He had no more cheese for Plagg anyway, so it had been his last transformation, but he had hoped that his lady would somehow manage something… From the voices he heard on the other side of the thick door, it seemed the only thing she had succeeded in was to protect him. But not herself. Then the voice… it was not exactly Ladybug's voice. He usually heard it in soft tones, but this broken intonation… it was not the first time he had heard it!
"No! Marinette! No, I can't lose you both! Please, Marinette, no!"
A tear rolled down Marinette's cheek and she looked up at Hawk Moth from the cold floor she was kneeling on.
"Hurry up, please," she said. "And take care of him afterwards."
"Really, Gabriel, are you sure you know what you are doing?" an old voice chided him.
Hawk Moth turned around. "Fu! How did you enter?"
"Does it really matter? You intend to sacrifice this young woman, don't you? To bring back your wife."
"Yes."
"No! No!" Adrien shouted, still hitting the door. Marinette winced. His hands were going to be bloody before the end of all this.
"Good. She's willing, everything's fine. Now, did you check if your wife was willing?"
"You old fool, how could I ask the dead?"
"I will give you a way."
Master Fu walked toward Nathalie and handed her a black bracelet. "Put that on, my dear, and call, 'Dark feathers, grow!'"
Nathalie glanced toward Hawk Moth and complied. She was transformed into an impressive woman clothed in black, with a black Venetian mask hiding her face.
"What's this?"
"The Raven Miraculous. Not a fighting Miraculous. No, no, this is how you will be able to ask the dead."
"Whom do you want to call?" Nathalie asked in a sepulchral voice.
"Emilie Agreste, my wife."
Nathalie raised her arms above her head, deploying her wings. The voice that came from behind her mask was now completely different.
"Gabriel? What is happening?"
"Emilie? Oh, Emilie!" For a moment, Hawk Moth was deprived of words. Hearing the voice of his beloved wife was too much for him. Behind the door, Adrien had stopped shouting also.
See, my love, that's why I'll do it. You miss her so much.
"Emilie, I have the means of bringing you back to me. Do… do you want me to?"
Nathalie, her arms still above her head, looked around. Strangely, her eyes were now green. She took in Marinette on the floor, tears running down her face, the closed door from which came a broken "Please…"
"Open the door."
"Emilie, answer me."
"Open the door."
-o-o-
Adrien bolted to Marinette's side and took her in his arms. She tried to resist him, protesting it was better that way, but he would hear none of it. He looked up at Nathalie still stuck in her strange pose.
"Mom, if you hear me, I love you, I do, but I love her too. She… I could go on because of her. She's all I have now. Please?"
Nathalie's strange green eyes turned to Hawk Moth. "What would you have done if your father had tried to kill me to save your mother?"
"I would have saved you and run away with you," he replied without thinking.
"In what is this different? Look at her! She loves him with all her heart and he seems happy with her. They look like us."
But Hawk Moth didn't want to see the similarities. His hand closed tightly on the two Miraculouses he held.
"If you do what you intend to do, Gabriel, yes, you will have me back. But you will lose our son and in time, you will lose me also, because I won't be able to forgive you for that. Parents protect their children, Gabriel. She is doing your work for you."
Despite himself, Hawk Moth looked at the two young people. Marinette was holding Adrien's face in her hands.
"I love you, always have, always will. But you cannot forbid me to do that."
"You knew who Hawk Moth was and who I was."
"Yes, I knew. But I didn't want you to know. I had hoped to spare you this grief. You would have found your mother back, your father would have been back to your side and I would just have… disappeared. I'm sorry."
She kissed him gently and wormed out of his embrace, facing Hawk Moth.
"Do it now, I can't stand it anymore."
Nathalie was fighting to keep her arms up and she was losing the fight.
"Remember, Gabriel," said Emilie, her voice sounding tired. "I love you, always have, always will…"
Nathalie collapsed on the ground as her last words floated in the air, in an eerie echo of Marinette's earlier promise. Hawk Moth took in the resolve on the young woman's face, the love in Adrien's face while he was scrambling to reach her, maybe protect her from his own father, then Nathalie's exhausted body on the floor and Master Fu waiting patiently for his decision.
"Nooroo, dark wings, fold," he said tiredly.
Then he looked at Marinette. "No," he said.
The end!