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