Here is the full list of all 28 Billion Beat achievements.
Beat Death Hand for the first time
Beat Punkito for the first time
Beat Dranx Master for the first time
Beat Tall Squan for the first time
Beat Swag Master for the first time
Beat Pugilartiste for the first time
Beat Ghetto Knight for the first time
Beat Mutant for the first time
Beat Fancy Squan for the first time
Beat Tronix Master for the first time
Beat Death Hand X for the first time
Beat the final boss for the first time
Beat Easy Difficulty in Story Mode
Beat Normal Difficulty in either Story or Arcade Mode
Beat Hard Difficulty in either Story or Arcade Mode like an adult
Cleared the Baby's Beat Tournament for the first time
Cleared the Brawler's Beat Tournament for the first time
Cleared the Billion Beat Tournament for the first time
Beat Story Mode for the first time
Beat Arcade Mode without losing a match on Hard like an adult
Beat all 3 Hyper Missions of a match
Beat all 36 Hyper Missions
S-Rank a match on Hard like an adult
S-Rank all matches on Hard like an adult
Achieve a combo of 100 or more
Beat a match without getting hit on Hard like an adult
Buy Tronix like a coward
Fill out the Lie-Berry