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