u/Egormagnificent

Hey hey! New here, LOVING the game right now just have a question about cores. Come characters I have an freely swap between all the core options, some only can swap one core and the rest are greyed out and some others (my best girl Emika) have all options greyed out yet you can swap for some currency. I wanted to explore using something other than balance core with her but I’m not sure if there is a free way to get other cores or do I HAVE to spend on it. Will that make it a permanent choice as in can I swap between other ones I buy or do you have to buy each time? Sorry for the long question, thank you in advance :)