Here is the full list of all 15 Gazing from beyond achievements.
Achieve bad ends for three times
First enter Hope Branch.
First enter the condition of the main branch
First click Game Start
Three heroines achieve Final End or Good End.
In the philosophical system, collect philosophical items.
In the philosophical system, collect Equinox Flower
In the collection system, collect the first item.
In the collection system, collect half of the total items.
In the collecting system, collect all items.
Unlock and play Clara DLC.
Unlock and play Happy Birthday DLC.
First enter Jade Branch.
Achieve bad ends for ten times.
In Jade Branch, first achieve Eureka end.