There is really no reason for Larcade's magic to not work on Natsu tbh. I don't believe we have seen characters attacking Larcade when he is using his magic. They are either stuck trying to fight it or they simply fall for it. Honestly speaking, Natsu shouldn't even be able to get off a spell if Larcade is fighting seriously and with intent to kill. DF Natsu certainly can obliterate Larcade but even though he can do this at will, he does not start the fight in that mode and larcade should be able to hold his own against Natsu. I mean, this dude didn't parry but literally stopped Kagura's unsheathed blade with 2 fingers, took attacks from enhanced sting and still had enough strength to crawl all the way to the guild, cast RIP on Natsu enough to immobilize him despite being in a weakened state, take attacks from Zeref without completely going down until zeref used book hax. If a weakened larcade can immoblize Natsu with RIP, then at full power, he could potentially use his spells to take down Natsu. However, I will not disregard the fact that Natsu himself was not exactly in optimal shape, and that Larcade doesn't seem to be able to use spells and attack at the same time. Seems to be the case considering he requested that Zeref kills Natsu while he is unable to move when he could have done it himself or at least attacked. I suppose one could argue that Natsu could perhaps fight RIP long enough to force a stalemate or a situation where Larcade has to dispel it, and then he can use that opportunity.
Well, I am likely in the minority, but I think Larcade will take this. Natsu does have a chance, but I think he will be on the defensive (trying not to fall to RIP) for majority of the fight, and won't necessarily get the opportunity to use DF and make the attacks he needs. I do need to check more on Larcade's abilities and drawbacks for more information but I'm sticking with him for now
