Summoners

Summoners (呼び出し人, Yobidashi-jin) are ability users that have the power to call and command a creature to aid them. In most cases, the connection between the summoner and the summoned creature is a deeply personal one, and there is a strict limit to how many creatures can even be summoned (one appears to be the norm, but there are exceptions). In addition, the summoned creature appears to represent some aspect of the summoner's heart or nature. Depending on the connection, damage to the creature or summoner may or may not be shared with the other.

Tatsumi Mino
Tatsumi Mino was the first summoner to appear in the series. He summoned a trio of female snakes, who he named Josephine, Roxanne, and Simone. He viewed them as treasured companions, and their connection was of a very strong nature: Minou felt damage suffered by the snakes, and could be easily controlled if even one of the snakes fell under enemy control.

Heisuke Matsudo
Matsudo uses his own blood and a pentagram designed to summon an Ayakashi from another dimension. They entered into a contract, with the Ayakashi (who answers to Kagami, after the late Risa Kagami) agreeing to obey Matsudo in exchange for his soul upon his death.

Ito Orihara
When neutralizing a charm, Ito Orihara closed her eyes and assumed a prayer-like pose, summoning a small, winged skeleton creature. The skeleton appeared to act as a guide for her power, directing it while Ito concentrated.

Kiyoderu Yuugami
Kiyoderu Yuugami used blood magic to summon Kamina, a large, bat-like demon composed of his own blood. Kamina was used primarily for flying long distances, though it was implied that Kiyoderu could produce different versions of Kamina with varying capabilities. Kiyoderu's blood had to be stored for at least three years before he could create a Kamina capable of flight and transport. Kamina appeared to have its own personality, but was still greatly connected to Kiyoderu: when Kiyoderu suffered a serious wound (faking his own death in the process), Kamina lost its form and collapsed.

Kakeru
Kakeru learned a summoning spell in order to prove herself worthy of studying under Michiru. As proof, she summoned an enormous minotaur demon. Though it was obedient, there was no obvious connection between them otherwise, and once Kakeru dismissed it, it was never seen again.

Kekkaishi
Among Kekkaishi, summoning is traditionally reserved for Legitimate Successors, and even then only those who have reached a sufficient level of training are taught to summon.

Yoshimori Sumimura
As part of Yoshimori's training to master Musou, Shimano trains him to create and summon his landlord, a type of clone that regulates power while the summoner is in the Musou state. After summoning his landlord in battle for the first time, Yoshimori names him Shiguma.

Masamori Sumimura
Masamori is unusual, both for a Kekkaishi and a summoner: he gained access to his landlord despite not having the traditional training, and proved capable of summoning multiple beings.
 * Kurohime: Though Shimano confirmed that Masamori did not complete Musou training, he identified Kurohime, the large, black fish that Masamori summoned regularly, as Masamori's landlord (Masamori himself only referred to her as his partner, which is common between Kekkaishi and their landlords).
 * Kouya: Using hair from Kouya's remains, Masamori was able to resurrect him. In exchange for breaking the seal that Tokimori Hazama placed on Kouya's mountain, he agreed to act as Masamori's guide.
 * Mudou: Using hair samples he obtained from Mudou, Masamori was able to resurrect a less powerful (and supposedly less insane) version to temporarily act as his guide.