Here is the full list of all 39 Gal*Gun: Double Peace achievements.
Give 500 Girls Euphoria
View Aoi's Ending
Get a Perfect Score on “Her Majesty Shinobu”
Get a Perfect Score on “Shinobu in the Window”
Get a 30 Combo of Ecstasy Shots
Fire 1000 Pheromone Shots
Get 100 Ecstasy Shots
Experience Your First Doki-Doki Mode
Give a Girl Euphoria
Unlock All Trophies
Experience Your First Final Doki-Doki Mode
View Your First Ending
View Shinobu's True Ending
View Maya's True Ending
View Sisters Route's True Ending
View Ekoro's True Ending
View Kurona's True Ending
View Patako's True Ending
View the True Love Route's True Ending
View All of the True Endings
Get a Perfect Score on “Maya's Demon Calling”
Get a Perfect Score on “Maya's Medical Care”
Get a Perfect Score on “Sisters' Odd Ritual”
Get a Perfect Score on “Demon-Attracting Balm”
Receive a “Perfect!” Score VS Shinobu
Receive a “Perfect!” Score VS Maya
Receive a “Perfect!” Score VS Shinobu & Maya
Receive a “Perfect!” Score VS Ekoro
Receive a “Perfect!” Score VS Kurona
Receive a “Perfect!” Score VS Patako
Receive a “Perfect!” Score VS Mr. Demon Veggie
Receive a “Perfect!” Score VS Mr. Demon Balloon
Defeat 100 Demon Girls
Make 50+ Girls Experience “Double Peace”
Fulfill 10 of the Girls' Requests
Collect All of the Panties From the Changing Room
Obtain All Images in the Gallery
Complete Profiles for Every Girl
Achieve Godlike Rank