Messiah no Ichi Nichi

is a Japanese light novel series written by Hiroki Iwata, with illustrations by Toshiyuki Sato. The series began publication on June 10, 2008 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
Her name is "Messiah". He is 145 cm tall and probably weighs lightly. A second-year student attending Ayamegahara Gakuin Middle School, still 13 years old. She is a young girl who looks like a child, and she often laughs. I laugh a lot anyway. But at the same time, my tears are fragile and I'm crying whether I'm happy or sad. That is the characteristic of Messiah, the sister-in-law of Warabo.

And it is probably the most special being in the world. Today, the usual day begins for Meshi Atoho, my sister Renko, and my sister Firefly. Messiah is treated like a lucky charm, Renko is admired as a cool student council president, firefly rain is feared as a demon, and Tamotsu is a day scared by female students. And the usual day to protect the Messiah.