The boss. He's the one who's kinda interested to the main character of the story. This time, he's getting his own story - the new guy who's pink eyes one is new so yeah.
Probably the same customer who scared Sihwa the first time he visited the coffee shop. Probably an ongoing joke that college students are always exhausted or an authors self insert. But regardless, you got a keen eye! I would have never caught that! I was low-key impressed~
the artstyle remind me of the dawn of the dragon