This comic references from the April 29th 2017 developer stream the moment at around the 1h25min mark.

The man on the left is Shaonian, who started with the position of Lead Numerical Designer before becoming the Lead Designer for GFL, an appropriate choice to co-host with Yuzhong for the anniversary, given the responsibility he has for the game's design. Based on what I'm reading, apparently the ass belongs to Kamie, who acted as the programming lead for the game (before becoming the executive producer for Neural Cloud, and getting Baalia as an avatar).