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