Here is the full list of all 29 River City Girls achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Reached Max Level.
Reach 100% completion.
Collected $5000
K.O. the secret boss.
Completed the game on Hard.
Completed the game with a secret character.
Parry 10 enemy attacks.
Attacked Mr. Rudis.
Was defeated in detention.
That wasn't very nice!
Destroyed all Sabu statues.
Find the keys in the junk yard.
Enter the Penthouse.
Defeated an enemy with a fish.
Completed all of Godai's quests.
K.O. Abobo.
K.O. Noize.
K.O. Sabuko.
Complete the game in Co-Op.
Enter the Mall.
Obtain an item from the Pawn Shop.
Catch a dodgeball thrown by your ally.
Catch a boomerang.
Defeated an enemy by hitting them with another enemy.
Equip a new outfit.
K.O. Yamada.
K.O. Hibari.
Destroy a vending machine.
K.O. Misuzu.