@Chocolate Oh, I didnt know that, this usage of の it's not often covered in text books when explaining the basics of の particle, if i'm not mistaken, maybe in later lessons, thanks a lot!

あなたといれば、どんな世界も怖くないや > As long as I am with you no matter what kind of world, i'm not afraid

What different translation would this sentence have if I change も for は, i am having a hard time to understand the nuance of も+negative adjective

あなたといれば、どんな世界は怖くないや how much of the meaning would change?