Here is the full list of all 37 Gal*Gun 2 achievements.
Unlock all other achievements.
Get every girls' phone number.
Have plenty of conversations with Nanako.
Upgrade your Pheromone Goggles to their final form.
Have plenty of conversations with Chiru.
Upgrade your Demon Sweeper to its final form.
Reach the Harem ending.
Finish Nanako's route B.
Finish Chiru's route B.
Reach Risu's good ending.
Finish Nanako's route A.
Give 50 girls euphoria with Lovestrikes.
Take a good look from below when you have a girl over.
Get stepped on by 50 girls.
Get kissed by 50 girls.
Call a girl over to your house for the first time.
Reach the ending for the first time.
Finish Chiru's route A.
Clear all of the Kamizono Sisters' requests.
Get stepped on by 10 girls.
Give 30 girls Striphoria.
Give 500 girls euphoria.
Use the Demon Sweeper to give a girl Striphoria for the first time.
Suck up 500 mini-demons.
Clear your first search mission.
Get kissed by 10 girls.
Perform a Lovestrike for the first time.
Suck up a Metal Kurona for the first time.
Clear your first Doki Dokie Mode.
Clear your first defense mission.
Suck up 100 mini-demons.
Give 100 girls euphoria.
Give a girl a snack for the first time.
Get 50 ecstacy shots in a row.
Get 30 ecstacy shots in a row.
Clear your first regular mission.
Get an ecstacy shot for the first time.