you have to have a bunch of subeta objects and take them to the fragmentizer here: https://subeta.net/explore/fragmentizer.php?act=
click to choose them and then click fragmentize to turn them into crystals, not all subeta items can be fragged though. [BR] BUT be very careful what you are 'destroying' make sure that your happy to lose the item. It is also not as simple as that, if you 'frag' very cheap/low rarity items you may not get any crystals at all, but if you frag higher rarity items r66 and above you will guarantee to get at least 1 crystal and maybe more. Always remember that you can buy crystals for around 4000sp each so its a bit of a gamble, and its not a quick process either.
What most people do is use the wizard tokens you win from the wizard quests and use the vending machines to get a lot of items that are usually 'fragged' but again, check the prices of the items you may want to keep some if your collecting plushies beanbags clothing etc. I hope you manage alright.