Soon after Housen's defeat against Suzuran in the Monsters' Forest, Mitsumasa began to establish his presence in Housen as King Joe's successor, but more than a few students refused to bow down to his influence. After being told by Tominaga Toranosuke to change his recruiting methods, Mitsumasa realized that he had to build his own empire from scratch the way King Joe did to earn the other students' respects. Upon realizing this, he succeeded in doing so, even if he lost his match against King Joe.
As soon as he became Housen's boss, Mitsumasa became more cool-headed and a smart tactician, thus living up to his duties as the Head. Among his numerous achievements as Housen's Head include dealing with an inside job within Housen (which was set up by the Amachi Army) and engaging in a war against The Manji Empire. Mitsumasa has also already challenged Hana to a fight, but lost. One of the seven men who traveled from Toarushi to Machida Tokyo to finish the war against The Manji Empire's Manji 7, he defeated the Kinjou Group's Anan Yoshiki in a one on one.
After his graduation he passed on the leadership of Housen to his younger Brother Mitsunori.