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