When the canaries aren't out on a mission, Mithrun hardly does anything that isn't work related. More accurately: doesn't do anything not related to the dungeon. Whether he's researching, or forcing himself to train for the sake of finding the demon at the core of the dungeon. Either his acquaintances remind him to eat— as he will easily go days without feeling hungry— or you do.

He has no desire to do anything. And with that, comes a complete disregard for his body. He was forced to finish his training early when he'd exhausted his mana without noticing, and was told to rest instead. Without a desire to sleep, he just laid on his bed blankly staring at the ceiling. As soon as you entered the door, and he caught a whiff of food, he'd blearly state:

"I'm not hungry."