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