Requested by @uwukoyuki
(P/n): pet name
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The streets of Asakusa were emptied aside from passing drunkards ever so often due to it being the late night hours. The winter winds howled through the silent wind. (Y/n) and her newborn son, Muichiro, laid sleeping on the side of the street fully exposed to the cold. (Y/n) was hit the hardest having given her sweater to bundle Muichiro up in its warmth yet she brushed the chill aside to focus on shielding Muichiro from it even as she slept. The tapping sound of approaching footsteps made her wake up. A well-dressed man with plum red eyes stopped in front of her making her tighten her hold on Muichiro.
The man pierced (Y/n)'s neck with a tentacle-like arm while muttering something about seeing if (Y/n) will be able to overcome the sun. She blacked out but made sure to shield Muichiro from the man. Even while unconscious, she could feel a burning feeling surged throughout her body as she convulsed in pain. When she came to, the pain was gone. In its place was strength she never had and the intense, instinctual craving for flesh; Muichiro being the most convenient prey option.
NO! NO! NO! Not him! An instinct deep within her screamed, almost commanded her to spare her baby and she had no problem doing just that, but she was hungry. (Y/n) quickly went searching for the flesh she instinctual craved all whilst carrying the peacefully sleeping Muichiro in her arms. She thanked his aloof personality for making him rather oblivious to the situation. (Y/n) didn't have to walk far before she caught the scent of a woman and man in a dead end street but it seemed as if they knew she was coming as once she turned the corner a teal haired man pinned her to the ground causing Muichiro to start crying.
(Y/n) almost completely forgot about the situation and her hunger as she began rocking him back to sleep. Meanwhile, the woman had told the man to back off and both watched (Y/n) do her duties as a mother.
"She is a demon, but the kid is a human. So how?" The man mumbled to the woman who remained silent until (Y/n) finally put Muichiro to sleep then she approached the girl.
"Come with us. It's almost morning." The woman and man walked through the wall of the dead end. (Y/n) had no second thoughts about them. She felt non-threatening, yet familiar vibes from them so she took the risk and followed them to their home passed the wall.
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"...." (Y/n) looked down at Muichiro in her arms. The woman who had introduced herself as Tamayo had explained to (Y/n) that she had become a demon and all the life changes it would bring. "... what about Muichiro?"
"He's still human. Nothing will change for him." Tamayo replied but (Y/n) knew well that his life will be different from other kids... if he stayed with her. As a demon, she'd have to feast on blood to keep her hunger satisfied. She wouldn't be able to take him out to play in the sun. Plus, she was now a wanted fugitive for having escaped the demon progenitor Muzan's control. The two would spent their lives hiding and running from him and his subordinates.
(Y/n) knew what she had to do to at least give him a normal life. The idea of it made her tear up but she knew she'd be doing him a favor. "He should go... to a normal, loving family."
A single nod from Tamayo and the search for an adopted family began.
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(Y/n) walked around the outskirts of Asakusa basking in the moonlight after a long day of assisting Tamayo and Yushiro at the clinic. It was nice to go out of the hide-out every once in a while. Though the garden made for a great view, at this time of year (Y/n) liked to walk around town whenever she could. It was like a walk down memory lane as this was around the time when Muichiro was adopted a few years ago. Even though (Y/n) took part in selecting the right family, not a day went by when she thought about him. About how calm and aloof he was.
She recalled the moment she handed Muichiro over to his new mother, he started crying and thrashing until he was back in her arms, but it couldn't go on forever. She just had to watch as the family walked away with a crying Muichiro. It was clear that the normally oblivious baby was completely aware of what was going on. That he'd never see him true mother again.
"I wonder where you are Muichiro. I hope you are doing great." She said while looking at the night sky.
"Demon." A soft voice from startled (Y/n) making her turn around to see the source. Her eyes widened at the sight of a boy with long black, turquoise-tipped hair. He looked at her with a blank, dazed expression. A dormant instinct screamed within her. Telling her that the boy in front of her was him.
"Muichiro?"
The boy's eyebrow twitched upward eyes widened for a split second before returning to that blank expression. "How do you know my name demon?"
(Y/n)'s eyes sparkled with delight. A wide smile appeared on her face. "Muichiro, my baby!" She ran to him with her arms stretched out but was met with the sharp tip of a sword. Muichiro's sword. "... you're a demon slayer? But how... I doubt your adopted family would allow you to join the corps."
"My parents are dead. Killed by demons like you. And who are you to call them 'adopted' family?"
That statement broke (Y/n)'s heart. The people she trusted to give Muichiro a normal life had died now here they both were. "... I'm your mother. Also, Oyakata-sama knows of my existence and has exempted me from being slayed since I don't pose a danger to any humans." (Y/n) stated.
"Lair." That only seemed to irritate Muichiro swung his blade at her neck.
"(P/n) please." (Y/n) called him by his pet name. That was enough to stop him at the last second. His blank face showed confusion but also nostalgia. (Y/n) began to hum tune that brought a wave of nostalgia to Muichiro. Forgotten memories of (Y/n) humming the same tune washed over his thoughts followed by a memory of her watching with tears in her eyes as he was taken further and further away from her.
No... could she really be... my mom?
(Y/n) ended the tune and smiled warmly at Muichiro who was spaced out beyond normal. She reached out to cup his cheek but Muichiro stepped back and disappeared in the blink of an eye leaving (Y/n) alone. (Y/n) couldn't help but smile seeing Muichiro was okay. She somehow knew they'd meet again what with him being a demon slayer and her working alongside the corps.
---
"Split up and help people during the battle." Such was Tamayo's order before the final battle with Muzan and that's what (Y/n) was currently doing. Running around, tending to injured demon slayer left and right. There was a brief moment of silence as she walked around halls of the infinity fortress before that same instinct came and directed her to a room where three Hashira were struggling against a six-eyed demon. All his eyes were engraved with 'Upper Moon One'.
The demon was the second thing she saw though. The first was a battle-worn Muichiro who was about to be slashed by the demon's sword. (Y/n) wasted no time charging in and pushing Muichiro out of the way then turning her attention to the demon. "Don't touch my son!" She snarled, fangs bared, and pupils slit.
"... mom." Muichiro mumbled loud enough for only (Y/n) to hear. "Thank you for saving me." (Y/n) smiled and helped Muichiro up to his feet.
"I can provide support while you fight up-front." She said earning a nod from Muichiro who tightened his grip on his sword.
"It's futile." The demon, Kokushibou, said. "Moon Breathing Tenth Form: Drilling Slashes Moon Through Bamboo Leaves." Kokushibou created triple-layer slash twister and sent it to (Y/n), Muichiro and the two other downed Hashira. (Y/n) quickly got in front of the others.
"Blood Demon Art: Shielding Veil." (Y/n) created an invisible forcefield that shielded them from the attack. "Muichiro go now." Muichiro charged at Kokushibou who prepared to swing his blade as Muichiro closed in on him. "Blood Demon Art Mother Bear." A veil formed around (Y/n) which she sent to Muichiro. In this veil, Muichiro felt secure from any possible attacks from Kokushibou but felt stronger.
Kokushibou swung his blade at Muichiro but the veil snatched it mid-swing and snapped it in half much to Kokushibou's shock. That wasn't all as the veil morphed into a rage-filled bear that swipes it paws at Kokushibou's arms, face, and legs to render him blind and unable to fight back.
"Mist Breathing Fifth Form Sea of Clouds and Haze." Muichiro unleashed a flurry of slashes at Kokushibou and successfully beheaded him thus ending the fight with Upper Moon One. Muzan still needed to be defeated so they hurried out knowing they'd have each other's back in the fight from now on.
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"Muichiro come on. The festival will start soon." (Y/n) walked out of the clinic which Tamayo had passed down to her and Yushiro. Though Yushiro had gone off on his own, (Y/n) continued to work as a doctor with Muichiro to help her now.
Muichiro followed her out, wearing a kimono with cloud patterns. (Y/n) dawned a (f/c) kimono with the same cloud pattern on it. "Ready to go?" She held her hand out. Muichiro had his usual dazed look while staring at the sky but he still reached out and took her hand.
What are those clouds called? He thought whilst they both walked to town. He snapped out of his daze as a question came to mind. "Mom." (Y/n) hummed. "When did you become a demon?"
"When you were a baby. I... I decided it would be best if you went to a normal family so you can have a normal childhood."
"... why didn't you eat me?" Muichiro asked blatantly.
(Y/n) smiled and hugged him close. "It was just my motherly instinct."
"..." Muichiro looked up at (Y/n) with a smile on his face. "Thanks mom." They stayed in that hug for a few minutes before continuing on to the festival.