Yoshimori is the 22nd Kekkaishi of the Sumimura family. Throughout the series, he is depicted as a lazy, stubborn, and headstrong individual who is deeply committed to protecting his family and friends, especially Tokine, for whom he has harbored feelings since childhood. In his younger years, Yoshimori was prone to crying and strongly disliked being a Kekkaishi. His attitude shifted significantly after an ayakashi injured Tokine's arm due to his failure to eliminate it. At the start of the series, Yoshimori often engages in baking, an activity he values more than his duties as a Kekkaishi. He dreams of becoming a patissier but faces criticism from his grandfather for this hobby.
Yoshimori's abilities as a Kekkaishi differ from those of Tokine. Due to his impulsive and headstrong nature, Yoshimori lags behind Tokine in terms of speed and accuracy. However, he excels in sheer power and stamina, capable of creating powerful and large kekkai that Tokine cannot form or would exhaust her quickly. Observations by Shigemori and Masamori Sumimura suggest that Yoshimori possesses vast untapped potential in his kekkai. Additionally, he can activate zekkai without prior training, though it only reaches its full potential when his emotions are at their peak.
Only three instances have shown him using his fully powered zekkai: during a fight with Kaguro, while saving his brother Masamori from a fatal attack, and after Hiura is severely injured. This state rejects everything he dislikes, including death. Hazama later reveals that this is actually a different technique called Shinkai, which Yoshimori could not use without borrowing power from a strong entity until then.
The death of Gen profoundly changed Yoshimori's perspective, motivating him to become stronger. Seeing similarities between Hiura and Gen, Yoshimori told Hiura to kill him first if he wanted to take a life. Initially distrustful, Yoshimori gradually warmed up to them as they fought together.
Recently, Yoshimori's power has undergone significant changes. Under his grandfather's guidance, Yoshimori trained with Shimano, a two-tailed cat spirit, to unlock his full potential. After weeks of training, he learned to enter a mental state called musou, where he is emotionally detached and highly focused. In this state, Yoshimori's efficiency increases exponentially, and he gains superior speed and accuracy compared to Tokine. He is now training to achieve "ultimate musou," which will not only unlock his full power but also allow him to summon his "landlord," a guardian spirit tied to his heart and emotions. As a sympathizer for Karasumori, he can communicate directly with the landlord.
By chapter 266, Yoshimori has summoned his landlord, Shiguma, and can enter the "Musou" state at will. In this state, he creates seemingly indestructible kekkai and numerous barriers without showing signs of fatigue. In chapter 273, Okuni informs Masamori that Yoshimori is an extremely rare human compatible with Karasumori, who can share his immense spiritual reservoir with Yoshimori if chosen, possessing the potential to destroy the world.
