@Haremmony
Pretty much. After playing about 170 hours I still didn't got Kos-Mos, in the end I got fed up with the game for a lot of various reasons including gacha, finished the story and put it on the shelf. Because I could've handled grind and endless time wasting via opening those cores if there was something to look forward, but considering quality of writing I've met while playing, horribly mundane progression of each blade, bad UI you have to just deal with, lack of any proper guiding or encyclopedia - so you have to look up locations of monsters online - I just gave up.
There is also other random chance, to transfer blades between characters in your party you need particular item, and that item is you have limited quantity of cause it doesn't drop from respawning monsters, you just find it on occasion and that's it.
Only other way to obtain such item is to get not rare blade but "common" blade of certain 4 star rarity. Completely develop them and release. The problem is that during all my gameplay I managed to get only 3 of those blades period, they are even rarer than rare blades.
Whole gameplay system is completely fucked up, I can go on and on, but regarding random chances - what above is all there is. Problem that it is literally game foundation and it drags whole game down so hard it's not redeemable.
But hey, it got waifus so people ate that shit up.