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