GOSH THEY SHOWED UP IN A PICTURE TOGETHER SHIPSHIPSHIP IT'S NOT LIKE IT'S JUST A ****ING PICTURE!
Luigi needed someone to pose with in that picture.
Seriously, I'm not even fond of Luigi and Daisy. But it's pretty much the cannon ship at this point so I accepted it.
The closest thing he really shows as a hint to having a crush is "just make sure you tell rosalina that
I got that one" after giving Mario the Battlerock Galaxy green star. And that could be taken as Luigi just wanting credit on something which if you think about it is pretty true to his character.
Mean while, Luigi and Daisy have: [From Mario Wiki]
"It has been stated that Luigi has a crush on Daisy, and the attraction appears to be mutual. In Daisy's second appearance in the
Mario series,
NES Open Tournament Golf, she served as Luigi's caddy, just as Peach was caddying for Mario, and as her trophy in
Super Smash Bros. Melee points out, since that point "some gossips started portraying her as Luigi's answer to Mario's Peach". They are often paired up in spin-off games: they are seen golfing together in
Mario Golf Toadstool Tour, are "buddy players" with good chemistry in the
Mario Baseball series, they appear together in the
Miracle Book pages from
Mario Party 6, and in
Mario Kart Wii, there is a giant, golden statue on the
Daisy Circuit that shows the two holding hands and dancing together, along with another of
Baby Luigi and
Baby Daisy. Their team names from the
Mario Party series include, "Steady Sweeties" and "Tango Tanglers", and when Daisy received her trophy from Luigi in
Mario Power Tennis, she says, "Hey, sweetie! I'll take that"."