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