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