Kimetsu no Yaiba/Demon Slayer Isekai. Female lead.

Kokushibo

Haku was ON THE CEILING?!? No, it was the floor. The distortion of the infinity castle was discombobulating. There was a fully decorated coffee table above her. The dishes somehow stayed glued above her. She attempted to sit up, but her body ached. She let out a heavy sigh. "What burdens you child?" Haku looked to her right to see Kokushibo sitting cross legged, six eyes staring at her. Haku closed her eyes for a moment and opened them. "I dunno, maybe that Muzan is going to try and use me to become immortal." She forced herself to sit up and noticed a bandage wrapped around her arm where Muzan cut her, and another spot where he had obviously drawn her blood. "Thanks. I assume you're the one who bandaged me." Kokushibo nodded. "We are to assure you remain relatively healthy and as intact as possible." Haku frowned. "So keep the guinea pig alive." Haku could almost detect a smirk, but Kokushibo remained neutral. "I have also been tasked with having you answer some questions for me." Haku narrowed her eyes. "I will only answer if I want to." Kokushibo did not listen to her protest. "First, do you know of the blue spider lily?"

"Yes."

"Do you know where it can be found?"

"Who knows." She lied. Kokushibo did not like her answer, but continued. "How do you know about us upper moons?"

"You wouldn't believe me anyway so why waste my breath."

"Try me."

"Pass. Let's just call it foresight." Haku waved her hand at him. Kokushibo was not pleased, but decided to let the matter rest for now. Haku could not handle any more mistreatment at this time. After a long uncomfortable silence, Haku stood up and headed towards the door to the room they were in. Kokushibo moved in front of her. "Oh come on, you think I can just get out of this place?"

"You need rest at this time. Your breath is still off and Muzan took quite a lot of blood." Kokushibo scooped her up and placed her into a futon with a gentleness that surprised her. "Someone else may be here when you wake." Haku really only worried about one demon. "If you send Douma, there will be hell to pay." Kokushibo was about to answer about her having no choice in the matter, but let the matter rest. Haku closed her eyes and quickly fell to sleep.

When Haku woke again there was indeed another babysitter. Her head was in the lab of none other than Douma. Kokushibo must have done this on purpose. "Ah, awake now are we? Our last meeting ended rather unpleasantly. Lord Muzan even scolded me." he pretended to pout, but Haku could detect the malice in his voice. She went to get up, but Douma snaked an arm around her waist and pulled her into his lab. "Come now. No running away this time." Haku was stiff as a board, but tried to relax. She knew he was deriving pleasure from playing with her. "What do you want Douma?" The demon hummed. "Let's see, Kokushibo-dono said you wouldn't answer his questions. So I think I'll ask my own. Tell me what you know about me?" Haku looked up at Douma. "About when you were human? Or when you were Upper Six?" He kept a creepy smile on his face. "So you do know! Tell me and I can confirm." Haku thought for a moment, but it did not really change anything at this point. "Well, you remember your human life unlike most demons. As a child you were deified because of your eyes. Your mother killed your father then herself. You only cared about airing out the room afterwards. You look down on everyone but you can't feel emotions anyway. Clinical apathy. Adds on to you being a complete psychopath." Haku did not get to finish as Doma grabbed her throat. She knew it was a touchy subject for him. "You speak so rudely for such a lovely little lotus." Suddenly, Douma's face was crushed. Akaza grabbed Haku from Douma, holding her in one arm. "Keep your disgusting hands off her. Besides, Lord Muzan said to keep her in good health." Douma regenerated almost immediately. "Akaza-dono! Good to see you." Akaza looked at him with disgust. "You can leave. It's my turn to watch her." Douma seemed like he wanted to stir up a stink, but ended up leaving instead. Akaza placed Haku on the ground but kept his arm around her waist. Haku looked up at him. "Thanks for that. He- well- he- before you took me he-" Haku trailed off. Akaza tightened his grip, getting the drift. He suddenly wanted to track Douma down and kill him. After a few moments he noticed his grip on Haku. He bashfully released her. He sat down and patted beside him. Haku took a seat beside him. "Douma is nothing but a disgusting creep. Don't worry about him. If he tries anything I'll kill him." Haku smiled at that. She knew Akaza would not be able to beat him realistically, but the thought was what counted. "The name you said before. Why do you know it and what does it really mean to me?" Haku looked at the floor. "I can't say much, but the name is important to your human self. I think it would be better if you remembered on your own." Akaza frowned and Haku cupped his face with her hands. "Just know you didn't want any of this, it was all Muzan." Akaza leaned his face into her hands and closed his eyes. "I like your scent. And not because of the blood." The intimate moment was broken when Muzan entered the room.