The motif of these paintings are related to Japan.
Yu's 3 drawings were printed on the book "ゼロからはじめる基本の鉛筆デッサン (Pencil Drawing Lesson for Beginners)" published in 2011.
This book explains how to draw by pencil.
The duck on both pages is Yu's drawing. The pages explain how to draw by shaking color off and drawing a line.
The cat on the right page is Yu's drawing. It describes the importance to check a skeleton.
The dog on the upper right corner is Yu's drawing. This page describes how to draw pets by using highlights to show solidity.