i really like how canonically yuu is genuinely supportive of grim wanting to be a great mage. if i recall correctly, even character voice lines point this out. and it seems like yuu dotes on grim a lot and defends him too??? yuu even encourages grim's ambitions whenever he declares wanting to be a great mage. and also when he does that boss-henchhuman dynamic. i mean yeah you can interpret it as yuu saying that being condescending and sarcastic as if they're talking to a child saying "when i grow up i want to be famous!" but like. i really think they're genuine when mc loves grim in their own way.

even if grim is usually a menace, he's become like family to yuu.

and i'm pretty sure grim feels the same way.

think about it this way. despite all the mess, all the unpredictability, the danger, and all the drama being in nrc. what's always the constant? yuu goes home at the end of the day to the ramshackle dorm (basically their home at this point considering they slowly but surely fix it up over time) and with who? “the great mage” grim. as the sole outcasts in that academy, they both sleep soundly knowing they will always have each other at the end of the day.