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