Itou Junji Kyoufu Manga Collection: Souichi no Tanoshii Nikki

In the summer, siblings Michina and Yuusuke Hirose visit their distant relatives in the countryside. Though they have not met in years, they quickly find that they are in for a relaxing vacation: they get along well with their cousins Kouchi and Sayuri Tsujii, there is a pool within walking distance, and the scenery is ever refreshing. There is just one blight upon this otherwise lovely trip: Souichi Tsujii, the bratty third Tsujii child and black sheep of the family. Nail-sucking, occult-loving, and utterly mischievous, Souichi's idea of amusement is anything that makes others squirm. Whether it is throwing curses on his cousins, bewitching his classmates, or replacing his teachers with living dolls, Souichi finds all kinds of ways to ruin the fun that he is left out of. But even with his own mystical powers, his havoc never lasts too long: for when Souichi causes trouble, it always comes back his way.