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