Something I've always wondered. If a person has been unable to speak since birth, what does the "voice" in their mind sound like?

Probably the voice that they are most used to hear.

Subaru is not the one to die, the person he tells that to is the one who dies.
Also over time I started hating Subaru.

I mean, in Isekai Quartet he trigger two times the curse and he was the one dying but like i said i don't read Re:Zero because Isekai is not my favorite thing.

Subaru does not die when he leaks RBD he just feels something grabbing his heart in a literal sense