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