The beast from within (a demon slayer x carnitrix male reader)

Y/N kocho was the youngest of the kocho family his older sisters kanae and shinobu cared for him deeply and would often worry about him when he came back to the butterfly mansion bruised from getting into a fight with other kids but what would happen when he met a watch......that was made to do one thing........terrorize the universe

also for Tamayo she is going to be 9 years old when she was turned she just went up to the size of who old she is in canon but when she met you she started to be in her small form more and also is able to be near you without the Carnitrix activating