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For now, I had decided to move back to the merchant guild area, where they finally gave me a Merchant Card and also a sack of money from all the mana stones I sold off. Apparently, the ones I can make are of the highest quality, so they were sold at a higher than usual price, that's pretty good but I don't really know why the Mana Stones I make are of a higher quality. I mean… I make them the same way that others make them.
I actually just took a book from the Ice Moon Sect, read it, and learned how to form magic circles in the ground named formations, configuring a formation out of specific runes in the floor wasn't so hard to make, and after that I managed to convert the piles of mana cores extracted from monsters into refined mana stones, without the impurities of mana cores.
Check "The Protagnist's Sister Is Actually the Strongest"!