https://gamefaqs.gamespot.com/boards/204208-xenoblade-chronicles-2/76340715
For more details, click on the link at the start.
I want to start out by stressing that I had nothing to do with discovering all of this. I was just lurking in the reddit discord server when someone by the name of Moosehunter started revealing stuff about the blade RNG algorithm, the NG+ blades, the OST and more. Hence all credits belong to Moosehunter. I'm just writing this so we have it all in one place. I take no credits whatsoever.
Party member and blade name spoilers up ahead.
There are 5 elements involved in the algorithm that determines what kind of blade you can get from a core crystal. These are: the blade base probabilities, the pity system, which type of crystal is used, your Idea Cloud, and finally LUK (the stat). I'll go through them one-by-one.
Blade base probabilities
Every rare blade that can be gotten from a crystal has a base probability rate. This includes blades like Wulfric and Vess who are gotten from named core crystals (you can release them and then get them back from the gachapon system). A list of the base probabilities can be found here:
https://pastebin.com/raw/dzuxLqGy
Note that Wulfric, Vess, etc. are not given. They all have base probabilities of 1 in each column. So why are there 5 different columns? Well, it turns out that the game chooses which column gives the base probabilities on your save file upon the creation of said file. So if the game decides to give you column 5, you will have high base odds for Godfrey, Perceval, Azami etc. while having low base odds for Vale, Agate and Ursula. KOS-MOS, the NG+ blades and the named crystal blades are the only blades with the same base probabilities in every column.
Myth 1: Some blades (like Godfrey and Azami) are more common than others (like Zenobia and KOS-MOS).
This claim is not completely true or accurate. In reality it depends on which column your save file has. In column 5 Godfrey and Azami indeed have high base probabilities, but in column 1 they have much lower base odds.
The pity system
Yes, there is actually a pity system in place to prevent people from getting RNG screwed too badly. Moreover this system can be used to determine which column your save file has (more on that later).
So how does it work? Every column has a set of 3 fixed pity blades. As you open cores without getting a rare blade, your pity counter will increase by a number that depends on the type of core used. Common cores give 5 points, rare cores give 25 points and legendary cores give a whopping 50 points. You get your first pity blade at 100 points, your second blade after 200 more points and your third one after 300 more points. Your pity point counter is reset every time you get a rare blade. The pity blades are as follows:
Column 1 - Godfrey, Agate, Boreas
Column 2 - Perceval, Azami, Adenine
Column 3 - Gorg, Perun, Electra
Column 4 - Kora, Nim, Finch
Column 5 - Vale, Ursula, Floren
With the exception of Azami (column 2) the pity blades all have low odds in their column compared to other columns (that's a relief).
This pity system is what allows us to easily see which column our save file uses. The first step is to put your blades in chronological order and see which 10(-ish) blades you got first. Your 3 pity blades should be there, as well as other blades with high base probabilities (on average). This should give you an indication of which column your save file might use. If you want to be even more certain you could release one of your pity blades and use legendary crystals till you get him/her back. If you had all 3 pity blades and released one of them, then it takes 500 points (10 legendary cores) to get that blade back. The next one takes over 35 legendary cores to get back (as far as I know the person testing this is still opening cores, RIP). Release blades at your own risk, because if you're wrong about which column your save file uses, then you might not see that blade again for a while.
For more details, click on the link at the start.
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