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