her father was a vampire
"I lost my dad‘s book,"
The book is made by last hero.
For some reason hero is only summoner puppet so he maybe betrayed humanity bcs tired of being manipulated by them.
it's not impossible, but the MC did mention the story seemed to be written by one of the hero's comrades and this comrade depicted him as a tragic character in the story. but who knows, maybe her dad was a researcher like her and was just researching the hero and happened across this book. we just need more chapters so we can find out for sure.
SO she was hero‘s daughter （￣へ￣）