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