Masamori Sumimura is a member of the Sumimura clan and a kekkaishi, a human with the ability to use the Hazuma style kekkai jutsu in order to combat enemy ayakashi. He's the older brother of Yoshimori and although he is a great deal more skilled than his younger brother, he wasn't chosen as the family successor, which he resented for a long time. This caused him to leave his family once Yoshimori was old enough to assume his Kekkaishi duties and join the Urakai, or Shadow Organization, and created the Night Troop, a group of ability users who usually didn't have family but were the organization's task force.
"You're kind, but you're still just a kid. I'm telling you you'll have to think logically, because there are a lot of situations in this world in which emotional thinking won't hold up. Do you think you could control your emotions? Do you still not understand the importance of this job? It's not just the school's neighborhood. But this city and all the lives of all the people in it are your responsibility. You've really got to wise up. You're the successor, after all. How long do you think you can run away by just being optimistic?"
-- Masamori scolding Yoshimori on his job performance as a kekkaishi.
During his time as a Kekkaishi, Masamori excelled at everything that was taught to him, so when he was denied the Houin mark, a small square that appears on the palm of the family's successor, he was devastated. Yoshimori was confused as well, because the mark appeared on his hand and not Masamori's despite his brother clearly being the more skilled and better kekkaishi. Masamori didn't let this setback control him, however, as he still performed his kekkaishi duties and took Yoshimori under his wing, often times working with him and the next door neighbor, another kekkaishi named Tokine Yukimura. His job as an ayakashi was to protect Karasumori from any ayakashi wanting to "borrow" it's power. Karasumori was basically a well of power under the Karasumori Academy. If wandering ayakashi arrived and stayed there too long, they would gain in strength, size, and speed, and become a threat to the surrounding citizens. Although normally regular humans can't see ayakashi unless you have some sort of powers, this wouldn't stop the ayakashi from attacking and sometimes even killing humans.
The Night Troop
After Masamori left and joined the Shadow Organization, he struck up a friendship with a man named Mudou who was seated on the Council of Twelve and a highly respected ability user. It was through their countless interactions and training sessions that Masamori thought up the idea of creating the Night Troop, in some ways to mirror Mudou's own similar group of ability users. The goal of the Night Troop was to accomplish and execute their missions without anyone noticing. Masamori recruited many ability users he knew and befriended working with and alongside Mudou and the Shadow Organization, ranging from adults to teens and even to children. Most of the people he recruited didn't have a home or a family to go home to, so the Night Troop became their home and Masamori gave them purpose. He was well respected and looked up to within the group, and when Gen Shishio and Sen Kagemiya first met Yoshimori, they were severely disappointed and shocked by the gap between the two brothers' skills, even going so far as to saying "How can you be his brother?" and other dialogue along those lines.
"Unlike you Mudou-san, I have no desire to reject my own self."
-- Masamori to Mudou.
Masamori eventually took Muduo's place on the Council of Twelve because of Mudou's betrayal. He became obsessed with power and killed an entire training facility of ability users on his way to consciously choosing to die and be reborn as a human ayakashi. Masamori took this betrayal personally and hunted Mudou down, believing that it was his right and duty to bring him to justice. After finally picking up his trail and following him to a specific realm, Masamori asked Yoshimori to stay on side of a portal to make sure that Masamori wasn't swallowed up and destroyed within the realm. Inside, Masamori came face to face with his old mentor and has some stern words for him, questioning his reasons for betraying everyone he knew and choosing to seek out power at any means necessary.
Mudou eventually realized that talking to Masamori wasn't going to sway his position, so the two engaged in battle as Yoshimori accidentally made his way into the realm. Masamori, who had been separated from Mudou, arrived in time to save Yoshimori after the latter attempted to fight Mudou to no avail, and disintegrated his old mentor with his zekkai ability. Yoshimori believed the fight over, but Masamori informed him of one harsh truth: Mudou was immortal and reformed himself from nothing almost immediately after. Masamori told Yoshimori how Mudou has a Spirit Reservoir in his body, meaning by killing ability users, he could absorb their power to strengthen himself and prolong his life. As long as he had energy in that Reservoir, he couldn't be killed.
As the battle drew to an end, Masamori began getting overwhelmed by Mudou's attacks as even his seemingly impenetrable zekkai defense was being broken through. Before long, Masamori was at Mudou's mercy and was about to be killed if not for Yoshimori's intervention. Through sheer luck, Yoshimori was able to tap into a vast amount of power he had to destroy Mudou's Destruction Balls before they could cut Masamori in half and forced him to retreat, giving the two brother's some reprieve. Masamori eventually caught up to Mudou and was told the truth about his defection, about how he had found a ruthless power within the Council of Twelve that had killed him time and time again, and that his pursuit of power was in order to be able to defeat this person. He then taunts Masamori with taking Karasumori's powers for himself in order to fight this threat before eventually being destroyed, along with the entire realm they were in. Yoshimori then uses a spiritual thread to pull Masamori out before he died too.
Powers and Abilities
Hazama Style Kekkai Jutsu
As a kekkaishi, Masamori has been trained in the use of the Hazama-Ryu style kekkai jutsu. This jutsu allows the user to create a cube of pure energy around an intended target, usually an ayakashi, and blow up the cube with the ayakashi inside of it. The only limitations to this jutsu are the user's stamina, skill, and imagination, as you can create your "base" on the ground and extend the kekkai up, you can create your base standing vertically up and extend the kakkei horizontally, you can create your base five feet above the ground, etc. Masamori can create many kekkai after the other, he can stack them on top of each other, he can create them as jumping stones in the air to reach higher targets or gain an aerial view of a battlefield, he can create thin ones that are capable of piercing through a target, and he can freely control what is allowed out and kept into his kekkai. For example, one time he encased a cup of tea inside his kekkai. He dropped the cup, which fell through to the floor, but the tea from inside the cup remained.
Nenshi: As a kekkaishi, Masamori also has access to Nenshi, which are spiritual strands of energy that manifest themselves from the users palms. These strands are then used most commonly to tie enemies up. Masamori has been seen using about four from each hand.
Shikigami: As a kekkaishi, Masamori has the ability to use Shikigami. These appear in the form of paper and are activated once Masamori puts a certain amount of power in them. Their uses and forms vary depending on the user and his or her intentions, but they can be used as messengers, clones, and workers, mainly to help restore the environment of Karasumori after a battle, and can take the form of dolls, birds, or humans. The duration, level of appearance, and overall time limit depend on the amount of power put into making the Shikigami and the level of skill of the user.
Zekkai is an expert-level technique of the Hazama style kekkai jutsu. This technique produces a powerful kekkai around the user's body and is usually in the form of a black sphere. It is a technique created through the domination of negative emotions, such as hatred, grief, or regret, and is a powerful defensive and offensive weapon. For defensive purposes, whatever would come into contact with it would be disintegrated, forcing enemies to give up trying to get in close and engage in anything within five feet of Masamori. The same reason it's so deadly is why it's so great on offense, as Masamori can simply jump by someone and disintegrate parts of their body. It's not an infallible defense, though, as powerful slashes of wind and Mudou's Destruction Discs proved strong enough to slice through it, and although it allowed him to survive the attack, Masamori was still banged up from being hit by a bolt of lightning.
Masamori is skilled at summoning spirits by making contracts with them. He uses these spirits to help him locate particular targets, give him some guidance, or just act as partner to him.
Kurohime: Kurohime isn't a spirit that Masamori made a contract with, but actually his Landlord that he can summon at will. Masamori can turn his power into an ocean and allow Kurohime to swim in, which allows her to locate the energy of a target for Masamori to save him the time of physically looking for them.
Mudou: Masamori used hair from the original Mudou to "resurrect" a younger version of Mudou that wasn't evil and power hungry. Masamori would often ask him for his opinion on certain situations as he valued this version of Mudou's wisdom.
*Kouya: Kouya was a wolf spirit that lived with Madarao 400 years ago on a mountain. Feeling betrayed by Madarao and humans, he chose to become an ayakashi after his death and attacked Karasumori. He was defeated Yoshimori took a tuft of his hair, gave it to Yoshimori, and asked him to take Kouya back to the mountain so that he could be buried there and finally have peace. Masamori agreed, and made a contract with Kouya and used his services for a short while. His sense of smell and his extendable, razor-sharp tail came in handy when Masamori went in search of Yumeji. Once Masamori believed he was done with Kouya's help, he took him to the mountain and released him.
Shakujo: A spear used by kekkaishi. This can be used as a melee weapon, a cane, but is mostly used for tenketsu, which absorbs the remains of an ayakashi to prevent it from regenerating.