Sojiro entered Eitoku Senior High, after graduating from the school's middle school. Him and his friends, the F4 controlled the school and were feared by the students and staff. Partly to amuse themselves, they began giving out "declarations of war" (a red card) to those who defied them, including Kimoto.
The F4 first met Tsukushi, when her friend Makiko Endo landed on Tsukasa Domyoji after falling down the stairs. Tsukushi protected her friend, earning herself a red card. However, she decided to fight back and declared war on the F4, which Sojiro and Akira found "spunky".
Sojiro and Akira teased Tsukasa about Tsukushi's similarity to his older sister, which offended Tsukasa and caused him to make his "next move." Ultimately, he decided to hire some students to assault Tsukushi. After hearing about it, Sojiro and Akira disapproved of his actions. They also questioned if Tsukasa was responding to the abuse he had taken from his sister. Sojiro and Akira later decided to stop bullying Tsukushi, believing it to be Tsukasa's vendetta.
After graduating high school, Sojiro began to attend Eitoku University with Akira and Rui. During his second year, he attended Shizuka's wedding in France. While continuing his education, Sojiro became the Grand Master of his family's tea house.