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