GIYU X SHINOBU [Finding Forever in Each Other Across Lifetimes]

Chapter 1: Where it all started.

Shinobu Kochou, one of the Demon Slayer Corps' most intelligent member, had always been fascinated by the power of potions. Her latest project was a potion made from the delicate petals of wisteria flowers, rumored to grant eternal life.

As she carefully mixed the ingredients in her laboratory, she couldn't help but think of her little sister, Kanao. She had initially planned to drink the potion herself, along with Kanao, but as she analyzed the potion, she began to doubt its effectiveness.

"Maybe this is all just a fool's errand," she muttered to herself as she stirred the potion. "Maybe I should just abandon this for a while and focus on my mission to kill the Upper Rank 2."

Shinobu carefully bottled the potion and labeled it with a note warning of its potential to grant eternal life. She placed it alongside her other important medicines and headed out to train again.

The Demon Slayer Corps had been called to the Infinity Castle, where the Upper Moon-ranked demons awaited them. The stakes were high, and the tension was palpable as the demon slayers prepared for battle. Shinobu Kochou, walked through the corridors of the castle, her heart pounding in her chest. She had a score to settle with one of the demons, the white-haired and rainbow eyed Douma, who had killed her beloved sister Kanae. 

As she rounded a corner, she saw Douma standing there, his fan in his hand. Her anger boiled over, and she charged at him, despite knowing that he was physically stronger than her. Douma merely smiled as he dodged her attacks, using his ice breathing to create a frigid mist that filled the air around them. Shinobu gasped for breath, her lungs struggling to handle the cold air.

"You're not so tough after all," Douma taunted her. "Just give up and accept your fate. You're just like your sister, weak and fragile." But Shinobu was not one to give up easily. She gritted her teeth and continued to fight, even as her body began to weaken. "You will pay for what you did to my sister," she spat out between labored breaths.

Douma merely chuckled. "Ah, yes. The girl who looks just like you but stronger. Is that...Kanae? I remember her well. She put up quite a fight, too. But in the end, she was no match for me. Well thanks to her, my tummy got full. Your sister is so... TASTY."

Shinobu felt a surge of rage at his words, and she summoned all her strength to strike him with her sword. As her blade sliced through his neck, she knew that she had used a special weapon - a wisteria-laced sword that she had been saving for just such an occasion. Douma gasped as the wisteria poison began to take effect, weakening him and leaving him vulnerable. But Shinobu was also feeling the effects of the cold air in her lungs, and she stumbled back, coughing and wheezing.

As Douma's body began to disintegrate, he reached out and grabbed Shinobu, slicing her in half with a final act of desperation. She fell to the ground, her life slipping away as Douma absorbed her body from his stomach. The other demon slayers rushed to Shinobu's side, but it was too late. She had given everything she had to avenge her sister, and in the end, she had paid the ultimate price. 

Kanao and Inosuke were both panting heavily as they watched Douma absorbing Shinobu's body. Kanao's eyes widened in horror as she realized what was happening. 

"No, no, no," she whispered, her voice shaking with emotion. "He can't be doing this." 

Inosuke, who was usually loud and boisterous, was silent for once. He was also horrified at the sight before him. As they watched, Douma finished absorbing Shinobu's body. Kanao couldn't hold back her tears anymore, and she started crying. "Why did she have to die like this?" she asked, her voice shaking. "She didn't deserve to die...my sister is gone." Inosuke didn't know what to say, so he just stood there silently, letting Kanao cry it out. 

Suddenly, they heard the crow announcing Shinobu's death. "Kucoow! Kucoow! Insect Hashira, Shinobu Kocho was killed by Upper Rank 2! Insect Hashira, Shinobu Kocho was killed by Upper Rank 2! " Kanao cried harder, and Inosuke felt a lump form in his throat. 

Giyu, who was fighting another demon at the time, felt his heart skip a beat when he heard the crow's announcement. He couldn't believe it. Shinobu, the girl he had feelings for, was dead.

As Kanao and Inosuke were grieving, they noticed that Douma was beginning to weaken. Kanao's tears turned into anger, and she stood up, ready to fight once more. The two did their best fight against Douma. Finally, they defeated Douma, who was weakened by the wisteria poison that Shinobu had injected into him. 

FAST FORWARD [6 months after]

Giyu Tomioka stood in the peaceful, serene setting of the Kamado family's old home. Six months had passed since the defeat of Muzan Kibutsuji and the Demon Slayer Corps had emerged victorious. But the price they paid was high, and many lives were lost in the battle against the demon lord. 

Giyu looked at his friends, the Kamado siblings Tanjiro and Nezuko, the boisterous duo Inosuke and Zenitsu, and Kanao, the younger sister of Shinobu Kochou, who had died fighting one of the upper-ranked demons.He couldn't help but feel a sense of melancholy wash over him as he remembered the losses they had all suffered. But he pushed it aside and smiled, knowing that his time with them was limited.

"Giyu-san!" Tanjiro shouted, running towards him with a smile on his face. "It's so good to see you!"Giyu smiled back and hugged the young man, feeling a warmth in his heart that he hadn't felt in a long time.

"I'm glad to see you too, Tanjiro," he said, his voice soft and gentle. The group spent the day catching up, reminiscing about their past battles and discussing their future plans. Giyu watched them all, feeling a sense of pride and affection for the young warriors who had come so far. As the day drew to a close, Giyu pulled Tanjiro aside and spoke to him in a low voice.

"Tanjiro, I need to ask you a favor," he said, his voice serious. "I want you to promise me that you will watch over Kanao and take care of her."

Tanjiro looked at him, surprised. "Of course, Giyu-san," he replied. "But why me?"

Giyu smiled softly, his eyes flickering with emotion. "Because I know... that you have feelings for her," he said. "And I know that if Shinobu was alive, she would have hit you on the back with a wooden sword for not taking care of her sister."

Tanjiro blushed and looked down at his feet. "I...I don't know what to say," he stammered. Giyu chuckled softly and placed a hand on his shoulder. "Just promise me, Tanjiro," he said. "Promise me that you will always protect her, no matter what. I failed to protect Shinobu, if I was only able to live for more years, I'd watch over her precious sister, but I can't."

Tanjiro nodded, his face serious. "I promise, Giyu-san," he said. "I will always watch over her. I'll never let anyone, or anything hurt her!"

Giyu smiled, feeling a sense of relief wash over him. He knew that the young man would keep his promise, just as he had kept his promise to protect all of them. "I have to leave. I'm going back to the butterfly estate and check over Aoi and Shinobu's three little assistants." Tanjiro, Nezuko, Aoi Inosuke and Zenitsu waved goodbye with their eyes a bit teary. 

"Have a safe trip Giyu-san! I'll always keep my promise!"