Younger Brothers’ Day, known as Otouto no Hi, is observed in Japan every March 6 to honor the bond between younger brothers and their families. The celebration was initiated by manga artist Kunio Hatada in the early 1990s, who aimed to recognize sibling relationships after studying the success of younger sisters in various fields. In addition to Younger Brothers’ Day, Hatada established other sibling-themed holidays, including Younger Sisters’ Day, Older Sisters’ Day, and Older Brothers’ Day. While it is less popular than Younger Sisters’ Day, the holiday is mainly celebrated by manga and anime fans who commemorate iconic younger brother characters from their favorite series. For instance, Uchiha Sasuke from Naruto and Alphonse Elric from Fullmetal Alchemist are notable examples. To celebrate, individuals may give gifts, share meals, or reminisce about cherished memories, often using the hashtag #YoungerBrothersDay on social media.