"Father," System said. "It seems as though there are three layers to the changes. I'll try to just add the first layer in the VMD."
"That's the energy collector core," Spagetti said. "When magical energies are harvested, they need somewhere to go. Rather than dispersing the energies and letting a new demon form elsewhere, the magic is directly siphoned off. It can hold a whole world's worth of energy." Huh. He knew a bit more than I thought.
"Replacing Layer One with Layer Two." System sure isnt big on testing, but I guess we're in a rush.
"That's the harvesting channels. Whenever there's a spike in raw magical energy, they work overtime in vacuuming it up and sending it to the core."
"Replacing Layer Two with Layer Three."
"That is the enforcement system. " Spagetti winced. "It's responsible for using the magical energy to make the Hero better at what he or she does. It's flexible enough to make anything, even a Rock Golem Hero, stronger. It's also what I immediately thought of when you asked about long term health effects. The magical energies are rarely at a perfect balance to be completely used up with reinforcement, and I honestly don't know what happens to the residual energies that linger in the body when they get back home. I used to think the energy just dispersed, but different worlds would have different Laws on how violently the dispersion would occur, if they have any regarding magic at all." So the Hero would become anything from a being with godlike powers to a mess of meat. Talk about a wide range of possibilities.
"System, run a simulation, titled Hero Simulation A. Apply the Heroic Gifts to my simulacrum and fill my simulacrum with the magical energies of Spagetti's world. Spagetti, let us know when the typical level of saturation is reached; the amount should equal the amount after the Demon King is defeated. We'll call it a Heroic Measure. System, fast forward until half of the energies are used to reinforce the body, since a typical Hero is sent straight home after killing the Demon King. Then model the result if I went to my original world like that."
The experiment ran. Spagetti told my System when to stop adding energies, and even corrected it regarding the typical mixture. He's quite a helpful assisstant.
Then we watched my body walk around, totally fine. System fast forwarded decades, then centuries, then millenia. There was no change. Ok, then. Magic wouldn't be a problem for me if I went back to my original world.
Then I had a thought. "System, use the same model but substitute my old mortal body instead of my current one."
We watched as the same thing happened. Immortal old me walked around, seemingly perfectly healthy. That wasn't good.
"Spagetti, ask your System how many worlds it selects from for the Hero summoning."
His eyes glazed over. "What!? You only select Heroes from one world!? That sounds stupid, there are thousands of them! Original operating parameters? Well freakin' change them! Now that's silly; you adopted the VMD readily enough. Wha?!"
He closed his eyes in frustration. "Apparently, while my System likes to adopt new ideas, it will not change the old without something breaking to cause it to fix it. Apparently, it says its original designer was big on the, 'if it ain't broke, don't fix it' mentality. And it only takes people from your world."
I nodded in agreement. "Very sensible, if you actually run tests every so often to ensure it's not broke. But that does mean there are a bunch of immortals running around my world. No wonder it feels like there's a giant conspiracy going on. Also, if your System rips holes in space so often for Hero summoning, it makes me wonder about the state of the fabric of space itself, as it's not so gentle with the tearing."
I sat on a rock and sighed. The rock molded itself to fit me. I looked around and saw the angel responsible. It looked and felt mightily pleased with itself. I beckoned it over. "You are now my official Chairangel. Go forth and set up a comfortable place to sit that won't interfere with the decor wherever you can. You are also responsible for my seating when I'm in Heaven One. If you need more matter manipulating techniques, you can request them from System."
It leaped for joy. "Yes Boss! Thank you for the opportunity to do something!" It crawled towards me and started to try to kiss my toes.
I yanked my feet away. "A simple kneeling bow will suffice. If you want to be affectionately grateful, I will take a hug or a kiss on the cheek." These were my children, born from my mind, word and will, after all. I did not mind being viewed as a father figure by them.
I felt a kiss on both my cheeks. A beaming Chairangel and a System angel stepped back and assumed flanking guard positions next to me. "I'll be sure to keep that in mind," System told me.
I looked to Spagetti, who was similarly sprawled comfortably on a rock. "While wandering immortals and spatial disruptions seem like not so great news for my world, nothing seems like it's preventing me from going a-Heroing for you. Except that I now have a burning need for a shawarma laffa."