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