@Podi125 @peppers she does know sign language. if you look at "the mute girl and her new friend" in the related section, it's the pre-serialization of this. and it shows she uses sign language when the teacher wanted to connect to her in chapter 9.
If I was the MC I wouldn't believe that my sister was dead and gone cause she managed to be reincarnated into his world once before. My ass would believe she could do it again. And I would study every binding/sealing spell and invent the strongest one so if I ever ran into her again I would be...