There is a moment early in the game where Shantae's Uncle describes the 4 playstyles of an adventurer.
Basically what he means by his description there are people who Complete the game, People who complete the game 100%, People who Speed run the game Any%, and people who Speed Run the game 100%
This achievement is for pulling off a normal Speed Run.
This game considers an Any% Speed Run as
Beating the game under 2 hours.
I recommend you attempt this achievement on New Game+ (Pirate Mode) as Shantae will start the game with all Pirate Weapons.
This makes skipping areas very easy you normally couldn't access them until later in the game.
There is some glitches and speed run strats on the 100% Run guide I posted