Waveshield through the pills.
Be faster when you react after the Nair. You miss a lot of stuff mostly because you land on him with Nair, then wait a second to react to his DI. That sort of reaction should be automatic. It shouldn't take, especially with a move like Nair with such little variation in trajectory, half a second to input a full jump Fair or whatever to finish the combo.
F-tilt is the essence of Luigi's ground game and should be used much more than what you're currently doing with it.
I would refrain from doing so many full jump Uairs and whatnot to pressure. Luigi's air-time is long, and he doesn't move much. Additionally, Desh seems to be capitalizing on this frequently enough (usually with Bair, which isn't pleasant to be hit by when your recovery is as amazing as Luigi's) for it to be considered a problem. I would advise spacing F-tilts or SH aerial wavelands (notably spaced Fair/Dair), double jump wavelands (notably spaced Fair/Dair), double aerials, and similar mixups in place of some of those full jumps. I can see the benefit of full jump aerial; it covers space somewhat effectively and covers jumps out of shield, which are common enough to factor in when choosing what to pressure with, but he's punishing you for them more than you're catching him with them, which makes it a vulnerability and therefore you need to use other stuff.
