Rank Requirement (or Rank Restrictions) is when certain items in the game cannot be bought in the Shop or Modifications Shop without meeting or going over the rank needed. Because not all items can be already bought when the player barely starts, he/she is naturally encouraged to play more to get promoted until they are able to get that item. Most of these items (that are rank required) are better than the rest in different ways, from firepower to even speed boost. Only rank required Primary Weapons can be used by lower ranks by picking it up from the killed player. After the Black Market opened, most rank required weapons and gear have NX Cosmetic Variants and slightly-improved variants for sale to any player of any rank, as long as they have the NX to afford it.
A drastic change in the game, was when more than half of the items in the game had their rank requirements upped. This included several Power Weapons, mostly all of those that were already obtainable to the player since the start (i.e. the L96A1 and the G36E). Other items, such as the special Combat Beanie and the IBH, had their rank requirement increased even more. This caused a very small improvement in the Combat Arms community, where lower-ranked players were forced to be more unique and use weapons and items that weren't considered overused or overpowered.