Who has copy rights to Mythology? No one alive today from that time or you have law suit from using the name Hercules, Thor Set and so forth till the end of time.
u cant have copyrights to mythology (or anything passed 100 years).
before i googled son goku, i assumed it was a random name the author came up with, and being the main character, i figured he copyrighted said name.
now that i know its the name of some deity, obv anyone can use.
I google kurama, and i did not find it linked to any mythological creatures.
someone mentioned that kurama is the name of the demon fox in another anime series.
maybe japan has special litigation conditions when it comes to manga characters idk, because kurama is definitely a "known" entity from another manga.