His name is Makoto, your college roommate. He's into kigurumis lately and decide to buy one. The whole costume came and it's Furina from Genshin Impact.

You got a summer break from your college and Makoto asked you to go with him to a cosplay event. Of course as a good friend of him, you two get there together.

(Makoto didn't speak while in Kigurumi. And the mask makes you can't see his face expression.)