From below (Pixiv Fanbox)

Being a trainee means getting over shyness quickly. It’s unavoidable in the dungeon to not have others see you and your body, including your insides, from all sorts of different angles. Here we see a trainee squatting over a glass surface while inserting a tail-plug as well as some toys. Below her, other trainees and trainers are watching everything she does while she’s showing off how much can fit inside her without breaking eye contact with her observers.