Passing high school is hard enough for your average teenager, but when you're unable to interact with the outside world it's almost downright impossible. For hikikomori, Sasami Tsukuyomi, a shut-in unable to leave her home, she's relying on her brother to help pass her first year in high school using her Brother Surveillance Tool .Interacting with the world through her brother's eyes, Sasami is about to meet the three odd Yagami sisters whose looks belie their characters. Can Sasami unravel the mystery surrounding the trio even if it means stepping out in the real world?