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|“||I will do away with them the moment they make a mistake. I will not allow any of these monsters near Karasumori.||”|
–Masamori Sumimura, Chapter 61
Masamori Sumimura (墨村正守, Sumimura Masamori) is the firstborn son of Sumiko Sumimura and Shuji Sumimura. While he excelled as a Kekkaishi, he was dissatisfied with the restrictions placed on him as a non-Successor, and eventually left home. He joined The Shadow Organization, founding and leading its Task Force (more commonly known as the Night Troop). Masamori is later promoted to the 7th seat on the organization's executive committee, the Council of Twelve, a position vacated by his former mentor Mudou.
Masamori is always seen wearing a Kekkaishi uniform while working, and prefers to wear a robe with an enlarged version of his Council of Twelve membership badge as an open challenge to those that might target him. He has short, black hair with a small crescent shape scar in the middle of his forehead. His eyes and eyebrows are very similar to Yoshimori's. He's tall and does not have the Houin mark.
Masamori maintains a calm, confident attitude around his family, but he is tough on Yoshimori, partially because so much is expected of Yoshimori as the Legitimate Successor, but also because he wants Yoshimori to learn to use his great power more responsibly. Masamori also has a habit of taking on highly dangerous tasks alone, such as trying to flush out traitors within The Shadow Organization, in order to protect his family and subordinates, no matter the cost to himself. He views his subordinates as family and takes any attack on them very personally. Inwardly, Masamori is greatly concerned about both the state of The Shadow Organization and protecting Karasumori (along with his family), and is sometimes forced to temporarily choose loyalty to one over the other. These heavy burdens often keep him alert and nervous privately, and also take a toll in the form of weight loss. However, he can also be cruel: to scare Yomi into doing his bidding, he threatens to terminate Yoki. 
HistoryAs the oldest son of the Sumimura Clan, Masamori was trained to become a Kekkaishi. When he was older, Masamori attempted to further his training. However, because he did not receive the Houin mark, he was denied access to the scrolls passed down by his ancestors, meant only for the eyes of Legitimate Successors. That Masamori did not receive the mark was source of resentment for him (and is most probably part of why he distanced himself from the family and joined The Shadow Organization), and confusion for Yoshimori (who believes Masamori is more talented and therefore should have the mark). As a child, Yoshimori drew the Houin mark on Masamori's hand in an attempt to cheer him up. Both brothers have a habit of staring at and flexing their hands: Yoshimori wondering why he has the Houin, and Masamori wondering why he doesn't.
Masamori served as Karasumori's Kekkaishi at some point after his mother's term, and Yoshimori began accompanying him at a young age to prepare for his own term (Tokine had already begun her own term at this point). Masamori stepped down the night that Yoshimori officially became a Kekkaishi, and was shown to still be a student at Karasumori Academy at the time. Some time later, Masamori left home and joined The Shadow Organization. Much of Masamori's career was patterned after Mudou, former Council of Twelve 7th Seat and someone that Masamori greatly admired. After Mudou abandoned the organization, Masamori founded the Night Troop, assuming command over Mudou's remaining subordinates.
The night that Gen Shishio transformed for the first time and ran away from home, Masamori and Kyoichi Hiba were called in to capture him. Gen seriously wounded Kyoichi, and then his own sister, but Masamori overpowered him with Zekkai. In order to help him control his powers, Masamori accepted Gen into the Night Troop.  When he first appeared in the series, Masamori had been away from Karasumori for about 6-7 years. 
Shakujō: Masamori typically carries a Shakujō while on duty. While primarily used to perform Tenketsu, it can also serve as a secondary weapon, a cutting tool, or a means of support when fatigued. However, it is fairly common for him to discard his Shakujō until it is needed.
Shikigami Paper: Masamori carries several pieces of paper, marked with the Houin, to create Shikigami as needed.
Powers & Abilities
Hazama-Ryu Kekkaijutsu: Masamori is repeatedly shown to be a very advanced Kekkaishi. His Kekkai tend to be much stronger than Yoshimori's, and he is the first seen using Kekkai as a bridge in mid-air (though Shigemori later shows that he is familiar with this as well). Masamori can produce large numbers of Nenshi and Shikigami all at once, and has enough stamina to use multi-layer Kekkai repeatedly in battle. In addition, his Shikigami are adult-sized and more humanoid compared to Yoshimori's, which are usually very short and pudgy.
- Zekkai: Masamori can also produce an extremely powerful Zekkai, capable of destroying almost anything it comes in contact with and protecting him from all but the strongest attacks.
- Landlord: He also has the rare ability to spread out his power in the form of a vast, dark ocean, which allows his landlord, Kurohime, to swim through it, creating ripples that detect the locations of enemies. This technique can be easily sensed by other Kekkaishi, and is even stifling to younger ones.
High Endurance: Masamori has notably high endurance. Though his Zekkai protects him from most attacks, he has still survived those strong enough to pierce it, even though they would normally be fatal blows without his Zekkai's protection.
High Spiritual Power: As with all Sumimura Kekkaishi, Masamori has a very large amount of spiritual power. He is able to use several techniques known to be especially draining in rapid succession without any visible strain. In addition, he is able to maintain his Zekkai for prolonged periods.
Summoning: Masamori has a talent for summoning and making contracts with spirits, particularly those of the departed. To date, he has at least two active contracts.
- Kurohime: Though Kurohime is Masamori's landlord (and therefore an aspect of his own power), he gained access to her through alternate means (Masamori was not allowed to attempt Musou training with Shimano).
- Kouya: Remade through the fur remnants of the original, Kouya somewhat reluctantly serves Masamori, in exchange for Masamori eventually breaking the seal that Tokimori Hazama placed on Kouya's mountain home. To symbolize their contract, there is a ring of x-shaped scars around Masamori's neck (Kouya is free to take Masamori's head if the promise is broken).
- Mudou: Supposedly a "good" version (or at least an earlier one, from before he began killing solely for power) of Mudou, remade from the hair of the original. At times he still displays the sinister, detached nature present in the original, but Masamori, while wary of him, still values his opinion at times.
- Main article: Yoshimori Sumimura
Since they were young, Masamori has held some resentment for Yoshimori for being born the Legitimate Successor of their family. He tends to be very hard on Yoshimori, though this is partially because so much is expected of Yoshimori and he does not always take his responsibilities seriously. The two brothers argue constantly when around each other, but they do care deeply for each other. Yoshimori inwardly admires Masamori and wants to be a powerful Kekkaishi like him, while Masamori is amazed by Yoshimori's seemingly limitless power.
|First Kekkaishi||Tokimori Hazama|
|Legitimate Successors||Yoshimori Sumimura • Shigemori Sumimura|
|Other Kekkaishi||Masamori Sumimura • Sumiko Sumimura • Toshimori Sumimura|
|Legitimate Successors||Tokine Yukimura • Tokiko Yukimura|
|Other Kekkaishi||Tokio Yukimura|
|Kekkaishi||Yoshimori Sumimura • Shigemori Sumimura • Sumiko Sumimura • Masamori Sumimura • Toshimori Sumimura|
|Ayakashi||Madarao • Shimano|
|Normal Human||Shuji Sumimura|
|Night Troop (Shadow Organization Task Force)|
|Leaders||Masamori Sumimura • Miki Hatori|
|Unit Heads||Makio • Kei Sazanami • Fumiya Somegi • Kikusui • Mukade • Aikawa • Atora Hanashima|
|Subordinates||Yukimasa • Gen Shishio • Hakudo • Odo • Dai Yaegashi • Todoroki • Takemitsu • Mother and Spirit Baby • Shoki • Shu Akitsu • Sen Kagemiya • Kyoichi Hiba • Hakota • Hakota's Mother • Ito Orihara • Shiragiku • Higurashi • Yomi Kasuga • Souji Hiura|
|Ayakashi||Raizo • Yaichi and Tsukinojou|
|Trainees||Misao • Akira • En • Haruka|
|Shadow Organization Executives|
|Current||Nura Kidoin • Tatsuki • Masamori Sumimura|
|Former||Nichinaga Oumi • Yumeji Hisaomi • Meian • Kusaribe Gaiji • Kagen Shiromi • Mudou • Ichirou Ougi •Okuni • Tsumugi Kazuchika • Konozuka Kihei • Juho|