The Akashic Engine is a continuous power source capable of unlimited energy production, albeit the output depends on how much you can extract , once a certain amount of the desired energy is gathered. It was created by a Advanced Technological Earth after a Magical Demon Empire breached the dimensions and invaded Earth. The engine contains no personality/mind and the prototypes of all Demon-Heart Series powers, but only about 1/12 of the strength.
Similar to all Demon-Heart Series, yours also have a backup containing all knowledge of Earth, but the blueprints of the others DHs are corrupted. It is still possible to reverse-engineer them from your Demon-Heart, but it will be challenging without the necessary know-how.
Alongside the Engine, you also gain the Manual of Operations, which, when followed correctly, allows you to upload your mind/soul to the Core and become a Demon-Heart yourself.