Here is the full list of all 42 GUILTY GEAR 2 -OVERTURE- achievements.
Kill 100 enemy capture units with your master in one match in battle
Open all of the hidden treasure chests
Win 3 times with Raven online
Finish one Tag Match (2vs2)
Win 20 times online
Win 3 times with Valentine online
Win 3 times with Sin online
Win 3 times with Ky online
Win 3 times with Izuna online
Win 3 times with Dr. Paradigm online
Win 5 times online
Win 3 times with Sol online
Lose 3 times online
Destroy the enemy masterghost on the first round of a online match
Finish one match online
Finish one default Free Mission with all masters
Finish Campaign Mode
Unlock Ky Kiske
Finish mission #18 "The Birth of a Girl"
Finish mission #17 "Demon"
Open 5 treasure chests in one match in battle
Open half of the hidden treasure chests
Finish mission #15 "Roaring Compass"
Kill 20 enemy servants with your master in one match in battle
Use any type of item 30 times in one match in battle
Slip on a Banana in battle
Open one hidden treasure chest
Finish mission #5 "Gaze of the Chronicle"
Finished mission #2 "The Alarm Always Rings Unexpectedly"
Finish mission #0 "Noise"
Finish Campaign Mode on Hard
Finish all default Free Missions using any master
Finish half of the default Free Missions using all masters
Finish all of the default Free Missions using all masters
Finish all of the default Free Missions using Sol
Finish all of the default Free Missions using Sin
Finish all of the default Free Missions using Izuna
Finish all of the default Free Missions using Dr. Paradigm
Finish all of the default Free Missions using Valentine
Get an S rank in all Campaign missions on Normal or higher
Finish all of the default Free Missions using Ky
Finish all of the default Free Missions using Raven