"It's okay to do anything to this hole, big brother..." So begins the strange story of a peculiar sibling relationship. The sister had vowed to remain a virgin until marriage, while the brother remained a cherry boy his entire life. However, their relationship operated under a special rule: penetration into each other's pussy was strictly forbidden, but anal sex was permitted. Under these conditions, they continued having anal sex for ten long years. This work portrays a unique love story, depicting the deep bond they formed over that time and the unusual dynamics created by their strange rule.