Rezarick

Rezarick is a Human Cleric-Accountant and a member of Black Sword Knights who serves as Isaac's adjutant (although he isn't actually the sub-guildmaster, and is instead its quartermaster).

In real life, his name is Kenta Yamazaki (山崎健太やまざきけんた), and he works as a cook.

Personality
Although appearing to be strict, Rezarick is actually a caring person. His personality, partnered with being a Cleric, makes him a reassuring presence during raids. Although he is a man of few words, he is earnest in his work and is attentive of other people's needs.

As the guild's quartermaster, he ended up shouldering the entire guild's administrative work on his own, and is suggested to be the one keeping the guild together behind-the-scenes, much like what Nazuna is to the West Wind Brigade.

Before the Catastrophe
Rezarick's real name is Kenta Yamazaki, and he is in his twenties, working early shifts as a cook in a lunch shop. Despite his young age, he excels in the art of cooking, and his food is the talk of the town. As a young man with such a reputation, he's had many offers to be set up with other peoples' daughters, and turning those offers down has become part of his daily routine.

Round Table Conference arc
Rezarick appears behind Isaac, both of them eating Crescent Moon's hamburgers.

When Isaac and members of the Black Sword Knights are going for a nighttime training session, Rezarick inquires about Marielle's and Shiroe's invitation to attend the Round Table Conference, and informs Isaac about Marielle's failed attempt to unite some of the small guilds. He accompanies Isaac to the conference and watches as the discussion unfolds. When the Black Sword Knights visit the Log Horizon guild building, Rezarick accompanies them despite not being a Summoner.

Ragranda Forest arc
Rezarick is one of the members of Black Sword Knights sent to accompany the beginners in their summer camp. He listens to Isuzu playing her lute with the other trainers. Alongside Log Horizon members Naotsugu and Nyanta, he accompanies the dungeon group to Ragranda Forest and sets up a temporary camp for the beginners at the dungeon's entrance. He becomes a reassuring presence for the beginners who are to challenge the dungeon everyday in order to gain experience.

He is the only member of his guild that went to Ragranda Forest, as the others went to Sand Leaf. When the group is attacked by waves of goblins, both he and Naotsugu ponder this unusual circumstance, with Rezarick pointing out that the encounter rate shouldn't be this high. Later, after setting up camp, Nyanta talks about how he spotted around an army of over a thousand Goblins, much to the player's shock. After Nyanta mentions that he couldn't contact Marielle or Shouryuu, Rezarick attempts contacting the Black Sword Knights members at the beach to no avail. Once Nyanta finishes his assessment of the opposing group, Minori and her group speak up, having heard the conversation. Serara and Isuzu contact the members of the Crescent Moon Alliance that were at the beach to learn of their situation. Shortly after, the entire Ragranda group gather in the tent to discuss their strategy. They learn from the description from one of the Crescent Moon Alliance members that there were "blue goblins" overrunning the beach. Although Rezarick asks if it was a coincidence, all three veterans are aware that it was most likely not one. He is present when the two groups meet back up, and attempts to dissuade Minori's party from going to save Choushi. When they do so anyways, he is part of the four-man group that goes to assist them.

Libra Festival arc
Rezarick is present by Isaac's side, and he and Misa are seen bowing to each other in respect.

Route43 arc
As Isaac's adjutant, he accompanies the guild master to one of several meetings with Shiroe about the plan to have the Black Sword Knights help train the Eastal knights in order to strengthen their relationship. After Isaac takes credit for doing the work that Rezarick did, he takes a sort-of revenge by calling Isaac "Isaac-kun," which the guild master detests.

Noosphere arc
Rezarick travels with the rest of the Black Swords to Maihama as part of the Round Table's agreement with Eastal to train the Glass Greaves, Maihama's knight order. After Isaac was sent to sit off to the side bor being too rough with the Earthling knights, Iselus begins bothering him. Rezarick joins them, teaching Iselus to call Isaac "Isaac-kun" ("Young Isaac" in Yen Press' translation), and laughs at Isaac's annoyance before returning to the training knights with Iselus.

Later, the three go into town together. Rezarick serves as Iselus' chaperone, accompanying him when he takes an interest in swords. When Isaac chides him for letting Iselus inspect a decorative, impractical sword, Rezarick replies that Isaac is a better judge of them. Shortly after, Calasin joins them; in response to Isaac's "what are you [Iselus], a kid?", both quickly retort that yes, Iselus is in fact a child.

Rezarick is present for Iselus' birthday banquet; when the Westelande assassins reveal themselves, Isaac tells him to hold them off as he takes Iselus to safety. Once Isaac dealt with the assassins that pursued him, Rezarick and Calasin arrive, with Rezarick offering to heal his debuffs.

Shortly thereafter, Rezarick, along with the rest of his guild and Calasin, have to deal with the Eternal Moths that invade Maihama until the conclusion of the Shibuya Raid.

Collapse of the Round Table arc
After Eins is named Duke of Akiba, Rezarick is seen convening with other Round Table guild members in Log Horizon's guild house to discuss the gravity of the situation. Per Rezarick, this development has caused much distress among the lords of Eastal, with Isaac going to Serjiad to explain things.

Nightingale's Song arc
Rezarick is one of the Black Sword members present in Akiba when the Genius Eirenus invades. He and his guildmates are the first to discover the Genius, who immediately cripples them by abusing the Teacher System to reduce their levels to 35.

Honey Moon Logs
During the Round Table Conference, Rezarick is seen trying to calm Isaac down after Shiroe reveals that he had bought the Guild Center.

Log Horizon SNG
Rezarick is a recruitable character in Log Horizon: New Adventure Land.

Equipment
Rezarick runs an Armor Cleric build, equipping a round shield and mace in battle. His full profile will be featured in Volume 12.

Trivia

 * Rezarick shares a voice actor with Lord Darte, HighlandSky, and Ragoumaru.
 * In a tweet made by Elissa, Rezarick supposedly worked in a morgue before the Catastrophe. When his official profile came out in the Log Horizon Database, however, it had changed to being a cook.