Dumb Sister (Original Version of the First World)

This article was originally the first world in the article "She's Just My Sister (Quick Travel)", but was later changed to Miko Sister. The heroine and story settings are different from the new version of "Sister", but because the mute sister is also a complete story that has been written, I put it here separately. [This story was written in May 2020, and the new version of "She's Just My Sister" was written in January 2023. There is a big time gap, and the characters and stories are independent. Intention: None