Yay! I got it!! It's so fun!! The first Nintendo app worth my time. Currently I have the original four that they give you as my set but I spent some orbs and I got Raigh, Tiki, and Hana
when you view their stats on the full page i accidentally touched their profile image when i was trying to go back and there were hearts and **** and it said they were talking but i had voices turned off so i have no idea what kind of gross anime tier stuff they were spewing at me
Shards and crystals, as far as i understand it, are for levelling up your characters. Red shards are for red weapons etc, yellow shards can be used on anyone.
Shards are for leveling until level 20, crystals for leveling after level 20
The yellow shards are universal between all character classes but they are less efficient than specific shards (If you have 480 red shards and you need 500, you can use 100 additionnal yellow shards. It's not the real numbers, it's just for example)