Yuutousei no Seifuku no Naka

"The well-behaved high school boy has a XX tattoo on his crotch—" High school student Yamada quits soccer due to an injury, and since then, he's lived a moderate, haphazard life, believing that those who aren't "lucky" only lose out if they try hard. Recently, Yamada noticed something. It was Sakurai, the well-behaved honour student and the luckiest person in the class, who was inexplicably cold towards him. He couldn't think of any reason why Sakurai, with whom he had no contact, would dislike him. Then, one afternoon after school, Yamada returned to the classroom to retrieve something he'd forgotten and bumped into Sakurai while he was changing. That's when he saw it… Sakurai's minimal underwear and the XX tattoo in a rather revealing place—!!?