One morning, I wake up...
"Where am I?"
"...who am I...?"
The protagonist, Tonomiya Masashi, has completely lost his memory!
While still not remembered my own name, I explore a completely unknown house I woke up in.
From there, I've gathered the following information:
Seems like I have three little sisters...
In addition, we live together in this private house and our parents are away traveling abroad...
...I, who lost his memory, suddenly living together under one roof with high school girls I don't even know...
What's more, they don't keep the distance between brother and sister at all...!
...will I able to stay within my reason...? (sweating intensely)
...and will I ever get my memory back?
[Translated from the official website]