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