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