According to what the PSO wiki says, LCK does not increase the drop chance and serves as a critical chance, but when I saw the drop chance that appears below the name/hp of the monsters, I remember that if you open the game in the cheat engine (not Ephinea itself but the base game), the character's luck (LCK) is directly linked to a variable (drop chance), which if you increase it to a very high value, basically any monster drops a red item immediately. then I remembered some ttfs I did with some specific players that changed the drop chances of the RR from dark falz, I thought it was just an impression, but I played on two different characters, one that had luck (lck) at 100 and another that was close to 20, and the chance dropped from about 1/186 to 1/184 and in others it dropped to 1/182 when I played with a guy who had about 60~80 luck, so I think lcuk is super useful but is overrated and unknown by many.