An idea for the skins. Make it so that you are able to equip/unequip certain variations of skins of different characters.
The skins would basically be different fits of the character from the show. They be different for shinies and normal units to keep the value of getting shinies.
For example the normal SUKUNA shrine skin could be changed to just yuji's torn clothing after SUKUNA fought mahoraga for the first time with the tattoos and stuff (reference A universal time SUKUNA). And then the shiny version/variant of the sukuna skin would be from the mid/late fight of Shinjuku showdown SUKUNA when he took off the haori/shawl and was in his loose clothing.