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