Yoshimori is the 22nd Kekkaishi of the Sumimura family. Throughout the series, Yoshimori is portrayed as a lazy, stubborn, headstrong individual who strives to protect his family and friends, especially Tokine, who he's had feelings for since childhood. When Yoshimori was much younger he often cried a lot and strongly dislikes being a Kekkaishi. Yoshimori's attitude greatly changed, however, after Tokine's arm was injured by an ayakashi that Yoshimori failed to eliminate. At the beginning of the series, he is often seen baking, an activity he often finds more important to him than his duty as a kekkaishi. He dreams of becoming a patissier, but is often chastised by his grandfather for this hobby.

Yoshimori's skills as a Kekkaishi differ from those of his counterpart, Tokine. Due to his rash and headstrong personality, Yoshimori has always fallen behind Tokine in terms of speed and accuracy. However, in terms of sheer power and stamina, Yoshimori excels. He is capable of creating extremely powerful and large kekkai, kekkai which Tokine is either incapable of forming or those which would quickly exhaust her. Throughout the series, observations had been made by Sumimura Shigemori and Sumimura Masamori that Yoshimori has an enormous wellspring of latent abilities in his kekkai. It has also been noted that Yoshimori is able to activate zekkai without any particular training beforehand. However, his zekkai could only be powered to its full potential in moments when his emotions overflow their boundaries.