つきツキ!

Tsuki Tsuki! (つきツキ！) is a light novel series written by Yujin Goto and illustrated by [[Korie Riko]], published in MF Bunko J. 

Synopsis : 

One day Shinobu wakes up just to find a naked blonde girl sleeping besides him. He has no memory whatsoever of her. Who is she? Why is she in his bed? Why is she naked? To make matters worse, his sister comes in and sees them. What will happen now? 
tsuki tsuki!