>>13118062>large amount of energyAn matter
There is no way around it, if you lose an arm and that arm weights 500grams of matter, you need to move 500 grams of something of your body to substitute that arm. Therefore demons should have very dense reserves around their body.
Now, the way to go about it is reducing other systems that clearly have lost purpose. Digestive? Dude I can extract energy from magic to sustain myself, eating people is just a plust to it, reproductive? Yeah like I care about children. Without those two systems, and with the due compensation in the endocrine, you can have both the space and energy require to at least increase cell regeneration to feasible levels but not popping out arms at a glance, more like growing that arm back in maybe a week or so.
Now in terms of the intrincate mechanisms behind that... it's beyond complicated. We don't have rapid regeneration not because our bodies like to linger with wounds around but because you need to make checks and adaptations as the arm grows, one way to see it is like trying to create a sand pile grain by grain, not only it will take a lot of time but if you are not careful something at somepoint is going to collapse the heap, and it's a big heap to make.
