Hehe, I dunno what made this artist think these two would go well together. But as MonK4 said, its only wish fulfillment on part of the artist. After Bowser tried to conquer the cosmos and harness the force of the Power Stars to make his own galaxy, I suppose the protector of the freakin' cosmos has some bad blood with him.
You know who I think would make an adorable couple? Luigi x Rosalina! If you think about it, these kindred spirits have so much compatibility! Possibly one of the most relatable video game couples of all time.
It's a shame Nintendo still let's him flounder around with that dull, marginal plank of wood Daisy. Really, Luigi could just keep in touch with Daisy and they'd be friends, much like with what's implied between Mario and Pauline. Luigi lacks confidence and his cowardice is quite prominent. He's capable of accomplishing great odds, even if he knows it. But he always puts himself down even for the sake of Mario, whom he swallows his envy for the sake of Mario's adventures.
Rosalina always brooded in her loneliness and became a little bit stoic from it because she longs for her mother. No one else, not even the Lumas, have ever gave her a bond to mend those feelings and make her feel cared. Even as Mario and the gang take her along for kart racing, sports, and even adventures, something still feels very off inside her. The Lumas and her friends, all a placebo numb to her ailing heart. You can imagine watching over the universe and raising her Lumas to become celestial objects is a lot of busy work, which exerts stress and responsibility on her.
You got one guy who thinks he's a loser. One girl who doesn't realize that people care about her. Troubled souls who sure could find some solace between each other. The potential for this pairing is huge and neither of them aren't scared to speak about it to the other. Plus, Luigi gets to be a daddy of all those adorable little Lumas! Who wouldn't want to chase those little wads of stardust around and play tag and hide-and-seek with them?
Needs more intimate pics! <3