Power Fusion is a mechanic in the Devil Children series.
Power Fusion is done by fusing items with demons, bestowing skills upon them. The items used can be found anywhere and obtained from demons. These skills can overwrite skills the demon already has as well. Myth Type demons can be fused with certain items, but not all of them. It is mentioned in Dark Version that Power Fusion originates in Fire Dem.
Take-Mikazuchi is the demon who oversees the Power Labs.