Disclaimer: Demon Slayer: Kimetsu no Yaiba and all its scenes, characters, etc. based on it, including the soundtrack, etc. belong to their respective owners (Koyoharu Gotouge, etc.). Cover image by MHA_ABNa on Twitter. I'm merely writing this to entertain and I don't get any profit out of this.
Note: Some time ago, before last manga chapters were released, I was thinking that if the worst happened and Nezuko couldn't be human again, she and Zenitsu would still want to be together and I came up with this story. I hope you like reading it as much as I loved writing it!
Always with You, like Lightning and Thunder
For as long as he could remember, Zenitsu had been afraid of death. How many times had he cried and kicked, screaming in terror, at the prospect of a demon killing him? He had never believed he would live long enough to grow old. And yet there he was now, on his deathbed, an old man.
Nezuko-chan lay beside him, sleeping. Since he had fallen ill, she had watched over him day and night. He smiled as he looked at her. Despite her appearance as an old woman, she was still beautiful and as strong as ever. As a demon, Nezuko was immortal, but she had gained control of her body in an amazing way. She had managed to speak normally again and hide her fangs and nail length. And in the end, she had managed to modify her body to be the same age as Zenitsu. She could not bear to see him grow old while she did not. He had told her a thousand times that she did not have to, but Nezuko had insisted and year after year her body had changed at the same rate as his. Even though they had not succeeded in making her human again, she wished to look like one more than anything else. He sobbed with emotion as he remembered and tears rolled down her cheeks. Nezuko had made her intentions clear the day she asked him to marry her. Because oh yes, he had asked her a thousand times, but she was not ready yet. As they got to know each other, however, they fell more in love.
Zenitsu always treated her like a normal girl, even at first, when she couldn't answer or understand him completely. In his dreams, Nezuko was like any other girl, she didn't need the muzzle and could talk properly. She also genuinely enjoyed his company and always smiled at him, making his heart flutter. It was wonderful. He had waited for that dream to come true for so long… When she finally learned to say his name he bounced around the room with joy and asked her to marry him again. She blushed without knowing why and, as always, she could not answer him, but he was so happy that he did not care. He kept talking to her as usual, helping her remember words and phrases, bringing her flowers and taking her for a walk in the field where they were blooming. There Zenitsu could finally make her a crown of white clovers, just as he had dreamed. When he put it on her, Nezuko was so beautiful that the boy began to cry without being able to stop himself.
"Nezuko-chaaaan!" he sobbed. "You are so kind and beautiful, if I could spend the rest of my life with you, I would be the happiest man in the world!"
"Th-thank you, Ze-zenitsu-san!"
Zenitsu thought he would faint at the sight of such a cutie. He put his hand to his chest and dropped to the grass. Nezuko bent over him with concern. When he finally managed to calm himself, Zenitsu stood up and their faces were closer than they had intended. They had never looked at each other so closely. The golden eyes of Zenitsu were caught in the gaze of Nezuko's pink eyes. He could not take his eyes off them, despite the blush on his cheeks, he could not look away even if he wanted to. A lock of her long hair had parted from the others and was falling from her face. Zenitsu raised his hand, hesitatingly.
"Nezuko-chan... May I?"
The demon girl closed her eyes and bowed her head slightly to him, giving him permission without needing words. Zenitsu reached out his hand, shaking slightly, and placed the lock of hair behind her ear.
"You are like a dream, Nezuko-chan."
She blushed, not opening her eyes, and moved closer to him, looking for the light and heat that Zenitsu radiated. It was like the sun that caressed her with its rays, soft and comforting. She leaned against him and the young man put his arm around her shoulders, resting his cheek against the girl's head. He wished that this moment would never end, that he could always stay by her side like this. Full of love and warmth. Pure happiness. There would never be anything he wished for more. And he was lucky because those moments with her kept coming.
Another day, while they were hugging, Zenitsu didn't think about it and kissed her on the forehead. When he realized what he had done, he panicked, fearing that she would not like it and walk away from him.
"Please forgive me, Nezuko-chan, I did not mean to disturb you!"
But she only looked up at his frightened eyes and, blushing, she put her lips to the boy's cheek, mimicking his gesture. Zenitsu felt an immense warmth envelop him and turned red as a tomato. Tears of happiness immediately ran down his cheeks.
"Nezuko-chaaaan! I am so happy, Nezuko-chan!"
She smiled. "Me too, Ze-zenitsu-san."
He embraced her tenderly again and she reciprocated.
Holding hands after a mission and going to the field to see flowers became a custom that both loved. When she could start talking more normally, they liked to play question games.
"Tell me, Nezuko-chan, what's your favourite colour?"
"Pink. What about you?"
"Yellow. I think it brought me luck after all. And what flowers do you like best?"
"Daisies and dandelions. What about you?"
"I also like daisies and wisteria. And... which boy do you like?" Zenitsu blushed a bit when asked, but waited eagerly for the answer.
She blushed as well but answered immediately. "I like Zenitsu. He is like the sun and a dandelion."
Zenitsu thought he would have a heart attack hearing that.
"Please marry me, Nezuko-chan!"
She looked at him perplexed. "You always say that... But... I don't know what it's like to get married. I don't remember."
Zenitsu realized he had never explained it to her and kicked himself mentally for being so stupid.
She hardly remembered her human life, of course she didn't remember what it was like to get married.
"When two people get married, they decide to stay together forever. They live together, eat together, sleep together," he blushed as she said this, but better explain that part another day.
"All because they love each other. They love each other very much and they don't want to live apart anymore. Husbands and wives care about each other's happiness and work on it day by day, as a team. It's something very special and very beautiful, don't you think, Nezuko-chan?"
"Sounds wonderful," she smiled.
"Then... will you marry me, Nezuko-chan?"
The demon girl thought seriously about it. She liked Zenitsu very much, but she didn't know if she could be a good wife for him. She still had to remember many things about being human.
"We can't, Zenitsu-san. Not yet. I need to remember more. Otherwise, I could not be a good wife to you."
"Oh God, Nezuko-chan wants to be a good wife for me! That's a yes! I'll wait for you, Nezuko-chan! I'll wait as long as it takes! And I'll help you remember! You'll remember everything!"
She hugged him. "Thank you for waiting for me, Zenitsu-san."
He sobbed. "Always, Nezuko-chan. I-I love you."
Nezuko felt a warmth she'd never felt before. She looked at his golden orbs. His cheeks were flushed and she felt hers burning too. But she didn't hesitate when she spoke.
"I love you too, Zenitsu-san."
"Nezuko-chan…" They hugged tighter. When they separated, Nezuko looked at his lips. She remembered what her parents did when they said they loved each other and, without thinking, closed the distance between them, pressing her lips with his while closing her eyes. The sudden contact took Zenitsu completely by surprise and his eyes widened in astonishment. This felt irreal. Tears of happiness were running down his cheeks as he closed his eyes and dared to enjoy that precious moment with his beloved Nezuko-chan. When they stopped to breathe, Zenitsu buried his face on her neck, crying. She caressed his hair with tears in her eyes. Their happiness was too immense to express with words.
So Zenitsu's crush had become the purest love you could dream of, and in the end, Nezuko had found out that she was as much in love as he was, remembering her human life more and more.
And they discovered that they didn't want to spend their lives with anyone else. They were like lightning and thunder, one always after the other, they could not be separated. They had saved each other's lives more times than they could count. They knew that they were willing to die for each other.
So one day, Nezuko asked him to go with her to the field where he had made her a crown for the first time and, blushing, asked him to marry her, to stay with her forever. Zenitsu froze. In shock. It took him a few minutes to process that. Then he raised his hand and slapped himself so hard that he almost fell over.
"Zenitsu-san!" Nezuko shouted, worried. "Why did you do that?"
"I am sorry, Nezuko-chan. I had to make sure I was not dreaming. Please, PLEASE, I beg you, tell me I am not dreaming. I'm still not sure. " He just didn't dare to believe that the waiting had finally ended, that his dream had come true.
She smiled, moved.
"You are not dreaming, Zenitsu-san. I want you to marry me."
"OH, MY GOD. OH, MY GOD, NEZUKO-CHAAAAN! I DO! I LOVE YOU SO MUCH! I LOVE YOU SO MUCH, NEZUKO-CHAN! I LOVE YOU!" He was crying my eyes out.
"I LOVE YOU TOO, ZENITSU-SAN!" In moments of intense emotion, Nezuko would catch the enthusiasm of her beloved, and start screaming like him. They hugged each other tightly and never left each other again.
The wedding was beautiful. A dream come true. Zenitsu spent half the ceremony with tears in his eyes. Nezuko never stopped smiling. All their loved ones were there, rejoicing over them. This was a historic event. The first wedding between a human and a demon. There was no greater symbol of peace. Tanjiro and Inosuke embraced them both, crying as well.
"Nezuko, my little sister, you look beautiful. Zenitsu, we are now officially brothers. You're going to be very happy, both of you."
"Buaaah, Monitsu and Nebuko! Congrats! You're gonna have lots of cubs!"
But the thing was they couldn't have children. Being immortal, Nezuko couldn't get pregnant. Although this caused them some sadness, they never cared. Because in the war against the demons, many of the children they rescued became orphans. And Zenitsu and Nezuko could not help but grow fond of some, even to the point of raising them as their own. Now they were all wonderful adults who loved them like their real parents. They couldn't have been happier to have raised those children. When the war was over, Zenitsu had finally managed to have what he always desired in his heart: the love of a family, of a wife and children who loved him. In spite of the pain, the difficulties... His life had been wonderful. Every second had been worthwhile.
Zenitsu grimaced and coughed. Old age was unforgiving. But he no longer feared death. He was happy. He only hoped he would not be separated from Nezuko-chan in the afterlife. He reached out and intertwined his hand with his wife's. She woke up and looked into his eyes, smiling.
"Nezuko-chan... You have given me a wonderful life. I'm only sorry I have to leave you."
"Zenitsu-san... I will go with you."
"You don't have to."
"Everyone's already gone. Tanjiro and Kanao, Inosuke... We'll join them. We don't need to be afraid."
"I will not. Never again, thanks to you. I love you, Nezuko-chan."
"I love you too, Zenitsu-san," she replied, kissing his hand.
Then Zenitsu closed his eyes, holding the image of his beloved wife forever, and didn't open them again. Nezuko got closer to him and kissed him on the lips. Then she embraced him and closed her eyes. And she did not open them again either. The demon woman had managed to control her body to such an extent that she could choose when to die. And she had chosen to die with her husband. She was the last demon and they were no longer needed. The two of them could rest together forever.
Zenitsu opened his eyes, but he was no longer on his bed. He was in a beautiful flower field under a bright blue sky. He was healthy again and his yellow clothes were spotless and perfect.
Nezuko was right behind him, a human again, in a beautiful pink kimono, smiling at him as always.
"Nezuko-chan… You came with me."
"Of course. We're like lightning and thunder after all."
He smiled and kissed her. Then they looked around, holding hands. Familiar faces appeared everywhere to greet them: Jigoro, Tanjiro, Kanao, Inosuke, Aoi... Zenitsu and Nezuko ran to greet them. They would never separate again.