Tadashiikaii no Karai Kata: Musubi no Nanatsu Ana no Himo

is a Japanese light novel series written by Hisashi Suzuki, with illustrations by Ichi. The series began publication on October 10, 2003 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
There is a cram school for elementary school students during the summer vacation. But I got up and set out on a journey. Because! My beloved sister-in-law, Rinko, is missing. Before Rinko left her house, she was scared of anything. I thought that I should be the only one to protect her Rinko and bring her back, but I wonder where to look. At that time, I met a guy called Kosaka Silk Thread. She's this guy, she has a nice face but she has the worst personality. She says, "Your sister-in-law is cursed." But this was the beginning of that strange adventure ...