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