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