This new Core followed on from a long string of realizations. Jake once believed that one Aether Core would suffice, and in theory it did. Only he came to realize that Aether was not a very readily available energy.
After more than a year of cultivating his Aether Core, it now contained enough Aether to blow up a small city, but this nearly limitless energy could not be mobilized as easily as in the early days.
Just like a black hole that swallowed more and more matter without spitting it out, his Aether Core continued to grow in density, accumulating more and more Aether, but it was trapped inside. The only Aether really available was the Aether contained in the Aether Core's accretion disk, which grew along with the Aether Core itself and reflected its pull on the surrounding Aether.
It took me a while to find a satisfactory energy system. I've read and seen so many manga, webnovels and anime that it's hard to be original on this aspect.
For those who are not very good in physics, the Joule effect is an extremely important property, otherwise the Reiga Core would generate so much heat that even Jake would not be able to stand it. Similarly to the Aether Core, the place Jake has chosen for his Aether Core will very quickly be replaced by an empty space, since nothing can survive inside it.
Unlike the Aether, however, the Reiga is a very real energy. Without using any spell, Jake will be able to use this pure Reiga to attack as a Naruto would do with Chakra. To put your hand in an advanced Reiga Core is like putting your hand in a ball of light of several million, even billion degrees.
If a default element was to be given to the Reiga, it would be Light.