Marius appreciates Louis for his human tenderness, his empathy, and Louis comes to Marius for paternal support. When they play strategy games like cards or chess, they’re among the best-matched opponents in the coven. Pandora’s at their level, too. All three have excellent poker faces. 

Marius finds Louis aesthetically appealing but doesn’t have any romantic intentions towards him, but even so, he can’t help but be curious about “upgrading” Louis. For how it might enhance Louis, but also possibly bc the act itself, the intimacy involved, is kind of tantalizing to think about ;] 

There’s fic out there that Louis has occasionally modeled in the nude for Marius’ paintings ;}

Canon quote under the cut. 

Marius re: Louis, when he’s consoling him that Lestat is still alive, in Queen of the Damned:

“He smiled at Louis. Something in the manner of this one made Marius happy, though he wasn’t sure why. He beckoned for Louis to come to him and they met at the foot of the table and walked together out of the room. Marius put his arm around Louis’s shoulder and they went down the iron stairs together, through the damp earth, Marius walking slowly and heavily, exactly like a human being might walk. 

“ ‘And you’re sure of it?’ ” Louis asked respectfully.

Marius stopped. “ ‘Oh, yes, quite sure.’ ” They looked at one another for a moment, and again Marius smiled. This one was so gifted yet not gifted at the same time; he wondered if the human light would go out of Louis’s eyes if he ever gained more power, if he ever had, for instance, a little of the blood of Marius in his veins.

…Then he embraced Louis again warmly. Just a little blood, and Louis might be stronger, true, but then he might lose the human tenderness, the human wisdom that no one could give another; the gift of knowing others’ suffering with which Louis had probably been born.”