Responses
Senou made that up. He never had a sister.
????
Chapter 2, he says everything was real and have a flashback about it
http://www.mangago.zone/read-manga/kakugo_wo_kimete/bt/227ae4b3142a61cd3241af54e2b3e426_chapter-2/pg-15/
then I guess she's fine. cause he says "he actually believed that?" idk. ╮(￣▽￣)╭
What about Senou's sister? Isn't she real and also sick? What happened for her to just disappear from the plot...?