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.
Completed the game on Hard.
Catch a dodgeball thrown by your ally.
Catch a boomerang.
That wasn't very nice!
Complete the game in Co-Op.
Completed the game with a secret character.
Reach 100% completion.
Reached Max Level.
Destroyed all Sabu statues.
K.O. the secret boss.
Parry 10 enemy attacks.
Enter the Penthouse.
Collected $5000
Completed all of Godai's quests.
K.O. Noize.
K.O. Sabuko.
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. Yamada.
K.O. Hibari.
Enter the Mall.
Defeated an enemy by hitting them with another enemy.
Attacked Mr. Rudis.
Destroy a vending machine.
Equip a new outfit.
K.O. Misuzu.