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