Lazy lore simple explanation:

im not gonna do the whole thing cause it would be a lot buuuut kazuki is one of many gods. He found a human, named kaito, on the verge of death once and decided to take him with himself. He made kaito imortal like himself and unable to die. Eventually kazuki got rlly curious of humans, how theyre build up, and how they work. Soooo what every "normal" person would do, he decided to cutely cut kaitos stomach open while the poor guy was still alive, wide awake, and could very well feel all the pain. He did that many few times and played around with kaitos organs, experimented, all that shiz. Maybe kazuki got a little too silly because he thought it would be a good idea to take a bite out of kaitos organs, and well he go addicted. ANYWAY i wont continue to type now cause im lazy :p (Praying this makes sense in the way i phrased it)

"GORE is interesting 👆 🤓 " ahh lore