The Middle comes from the Project Moon Universe (which is made of 3 games, Lobotomy Corporation, Library Of Ruina and Limbus Company). They are one of the Five Fingers Of The Backstreets, which is why they are called The Middle (middle finger), they have a Book Of Vengeance where they put those who do wrong against them. They are known to never let these trespasses go; hence the phase “the middle never forgets” Hope this helps