Here is the full list of all 15 Office Battle achievements.
Level all the skills up to 5th level
Reach 55th character's level
Knock 5000 people
Perform ‘To the moon’ 100 times
Knock 2500 people
Perform ‘To the moon’ 50 times
Sell 200 items in the shop. Without using "Sell all" button
200 knock-outs in 1 round
100 knock-outs for 1 round
Perform ‘To the moon’ 10 times
Strike critical damage 100 times
Level any skill up to 5th level
Buy 100 items in the shop
50 knock-outs in 1 round
Knock 100 people