You know, since it doesn't look like they hate each other, whys this guy don't just give back Yuki's body parts, take off his own heart, give it to the kid and call it a day? Everyone wins.
@EmptyBox Taking out the heart might make the kid dies permanently. You can't be sure that replace the heart with another will have the same effect. Ringomaru is a doll while that kid is a corpse so there are some differences in their immortality.
"Must have seen a rat or something." @EmptyBox "Eh? Don't wanna". Also extracting heart might not be the safest of procedures. Especially if it potentially became the core of existance.