Lake of Silver-Gray (Blue Archive) (Pixiv Fanbox)

After again messing up, Marina got a very harsh punishment, that is to retrieve a golden moustache from the bottom of an ice lake. She managed to do just that, but going back to the surface is a different matter, especially finding the hole she dived in. After getting lost for a while, she saw something strange... it's a small doll that's carried around by Sensei! With that as the guide, she managed to find the hole, and everything went hunky dory!