So I just found out about this now, a few hours before my copy of the game arrives in the mail. When you start a new game, you're assigned a "charm table," which is basically a list of what possible charms you'll be able to find in your game. In MH Tri and 3rd, this table got reset every time you turned on the game. In 3U, it's permanently fixed to whatever it is as soon as you confirm your character customization.
This means you can get screwed over out of a lot of end game gear by an invisible dice roll the game never explains to you. To add insult to injury, there are even cursed tables that give you than even the worst of the normal ones.
Basically, you want to play the game normally up until you obtain the first fishing ship. You then want to send it to Moga coast, using a Fish Finder in the process to get better results for the table, and waste two in game days. This is done by doing the Kelbi Horn delivery quest twice, which requires you to deliver two kelbi horns to the quest box, and as a reward, gives you two kelbi horns for your personal inventory. These can be used to complete the quest immediately so make sure you put them in your inventory instead of sending them to the storage box. This makes a five minute mission take five seconds.
Now talk to the fishing lady again, and note the pattern of the rewards from the fishing ship. Which item is in which slot, and how many of each item is presented as a reward. Then input those results into the table above. For the best results, you want to repeat this whole process at least 9 times. If done fast, the whole process takes about 30 minutes.
The most balanced and preferred table seems to be Table 10. The second best is table 6. But what if you want to main a specific weapon? Certain tables have better benefits for specific weapon classes. Whats been determined so far:
Table 4 and Table 6 favor Great Sword users.
Table 4 and Table 10 favor Lance and Gunlance users.
Table 10 favors Dual Sword and Hammer users.
Table 14 favors Switch Axe users.
Or if you want to see what unique charms each table offers, you can also use this convenient Google Doc. If you don't get the table you want, make a new character and repeat.
And before you drive yourself batshit insane trying to get the best table, keep in mind that this is . Most of this is only for the most hardcore players who want the best end game gear.