His Only Weakness (Demon Slayer x Reader)

Threat

The next night, I send a crow to Amane telling her of my engagement, but the letter that I get in response is completely unexpected, but definitely not from Amane.

                 Y/N,

I don't care for the fact that you're engaged to the Demon King or are a

Relative of the Master. You need to die for disobeying the rules.

I'm coming for you, and your children.

After reading the letter a couple of times, I quickly run around and pack stuff. However, it seems like luck isn't on my side because my house comes crashing down. I look around for the attacker and see them headed for Sakiya's room. Out of panic, I call for Nakime.

"Nakime, take Sakiya and the twins away somewhere safe!" And just like that, I hear the sound of a biwa and the smell of my children has disappeared, but their smell was immediately replaced by the smell of Upper Moon One. While I focus on the person who destroyed my house, I make a run for Kokushibo dodging the attacks thrown my way.

"Kokushibo, help!" Upper Moon One immediately appears beside me as he parries an attack.

"Y/N-sama. . .go to the fortress. . .I will get rid of these people before. . .gathering your remaining. . .belongings." I nod.

"Nakime, please take me to my children and summon Muzan." The familiar sound of a biwa transports me to the meeting space. As soon as Muzan appears in front of me, I engulf him in a hug and begin crying.

"Y/N, what happened?" I hand him the letter for him to read.

"Y/N, I don't care for the fact that you're engaged to the Demon King or are a relative of the Master. You need to die for disobeying the rules. . ." He rips apart the letter before throwing it into the void of the Infinity Fortress.

"K-Kokushibo is fighting th-them right now in the ruins of my h-house."

"Mommy? Daddy? Where are we and why aren't we at home?" We both tense up at her question. I quickly scrub away my tears.

"Sakiya, this is going to be our new home for now."

"Yay! I get to see Nakime-nee-chan everyday now!" I smile at her positivity. All of the sudden, I hear Nakime strum her biwa. Kokushibo appears, but his clothes are completely ripped.

"What happened?" I run towards Kokushibo.

"Those stupid demon slayers. . .are dead, but. . .they burned all of. . .your stuff. I'm sorry. . .Y/N-sama." He looks down.

"It's fine Koku-kun, as long as you're not dead. I'll be fine if I lose my stuff because I can always buy it again, but if you died, I would be left feeling guilty. Plus, where will I find another Koku-kun? Last I checked, I only know one Koku-kun!" He looks at me wide-eyed, before bowing.

"I will. . .take my leave now." I nod and he disappears.

"Y/N, we need to talk. Sakiya and the twins will be fine with Nakime watching over them."

"Okay." He grabs my hand before we are teleported to his room.

I sit down on the bed in the room before looking up at him. "What is it that you want to ask me?"

"I need to talk to you about the Blue Spider Lily. I want to be able to walk in the sun with you and the children. Please tell me where it is."

I tense up at the question. "Do you really want to know?" He nods slowly. I take a deep breath. "The reason I'm the only person who knows about the Blue Spider Lily is because my family protected it, now I protect the flower."

"What? Y/N, please stop speaking in riddles."

"I'm not. I am the Blue Spider Lily. My father did surgery on me when I was younger and placed the flower directly underneath my heart. In order for you to get the flower, you would need to kill me." I look into his eyes while he stares at me in shock. He cups my face in his hands.

"Standing in the sun is worthless if I can't be with you. I can't bring myself to hurt you." I smile at his words before he plants a soft and sweet kiss on my lips.

"I love you, Muzan."

"I love you too."

I smile before standing up. "Let's go back to the kids. I need to feed the twins." He nods and grabs my hand before we teleport back to the meeting room. I walk over to the crib before grabbing a bottle of milk that I left in a bag on the side of the crib. I hum a lullaby as Haruki drinks her fill of milk before feeding Haizaki.

"Y/N, you should go to my room with the children and get some rest. There's an Upper Moon meeting tomorrow and I need you to be at full energy. I'll be in my lab room if you need me. Nakime will wake you up."

"Okay." I put Haizaki back into the crib before Nakime transports us to Muzan's room. I tuck Sakiya into the futon before I find some spare covers and lay them down on the floor before I lay down and drift off into a dreamless sleep.

Taisho Secrets:

-Kagaya was made aware of the situation

-The Hashiras are hunting down whoever attacked your house

-Kagaya told the Hashiras that you are safest with Muzan