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