I suppose the Raid Suits could be old Void Century technology that managed to survive to the present day? That feels like one possibility, anyway. Some sort of Void Century clothing factory managed to survive and they used it to make the Raid Suits.
Given how "Sentai/Ranger" coded the Germa are, it could be something else. Maybe something tied to the Abyss Mark system? A lot of the Germa's powers do seem similar enough to the God's Knight's abilities, that they could be related, to a point. I could see one inspiring the other, at least. Using the "power of darkness" for "justice" is a common enough trope in stuff like Super Sentai and Kamen Rider that it could be a reference. The Numbers they all have might not actually be just for "style". Maybe the the Numbers are actually the power source, if they're using some form of "Symbol Magic". Their Numbers are their version of the Marks and Contracts. Just...worse, because the Germa are copying the real power of Imu.
But, I am leaning more towards ancient Void Century technology, myself. Maybe back then, EVERYONE was wearing Raid Suits for everyday life! Maybe it was the hot new trend, in the Void Century.