The current effects of [Rapid Fire] is unknown as well as it's scaling.
No known Alterations at this moment.
[Rapid Fire] first appeared in Arc 2 Chapter 24, where it is said to be a Tier 3 Palladium rarity Active ability similar to [100% Full auto] from Seeker's Revenge.
There are currently no known users of this ability and the amount of copies that are available for taking is unknown.