A teenage girl born from the Hīragi family. She joins the Hyakuya Sect to oppose her family. Saitō tells her to become a vampire and though refuses to turn her himself he helps Mahiru whilst also keeping his own objectives a secret.
A young seraph with high experimental potential. He acts as a leader toward the other orphans and is considered to be charming. He is half-Russian with blond hair and blue eyes. Saitō gives him money to buy ice cream. Mika's mother was a member of the Hyakuya Sect and gravely injured him by throwing him out of a moving vehicle. His parents died during the subsequent car crash and Saito delivers him to the Hyakuya orphanage.
A young seraph who Saitō picks up after his mother attempts to burn him alive in their apartment and then lights herself on fire and commits suicide. His father was also abusive. Saitō takes him to the same orphanage as Mika a few minutes before the Apocalypse begins, and Yu fights him the whole way. At some point he orders his men at the Hyakuya Sect to infiltrate the building in Osaka where he is being held disguised as Kureto's scientists in order to capture him which he retrieve him successfully.
The heir to the Ichinose family and one who opposes the Hīragi family. Saitō encounters him multiple times after a weak attempt to assassinate him, repeatedly offering an alliance persistently. Ferid later reveals that Saitō was only using Guren to his own benefits all along.
Sika Madu, the First Progenitor, was the one who turned Saitō into a vampire. According to Saitō, he disregarded almost everyone in the vampire race except for Ashera Tepes, because he was bored and was not interested in them anymore. Later in Chapter 81, it was revealed that he possess a strong desire to obtain the first progenitor's attention and to be truly "seen" by him and even going to extreme lengths in order to accomplish this goal such as sacrificing his his subordinates of the Hyakuya Sect and his own sired vampires by stealing their life force to strengthen his own power in order to battle the First Progenitor on even ground and finally obtain his attention. As noted by his fellow Second Progenitor, Urd Geales he has been attempting to accomplish this goal since the early days of their immortal lives which he has continued to do so up to the present time and has gone great lengths to accomplish this goal.
Saitō turned Ferid into a vampire. He disregarded Ferid because he did not act according to his expectations.
Crowley was turned into a vampire using Saitō's blood. It is unknown if Saitō is aware that Crowley is sired from him.
Saitō meets her while she is imprisoned in Ferid's mansion. She recognizes him as the one who tagged behind the First Progenitor and he talks to her about how the First was only interested in her brother Ashera Tepes.
Urd meets Saitō at Ferid's mansion while Krul was imprisoned. He addresses Saitō as Rigr Stafford and cuts off his arm. Saitō asks if Urd is bored following the laws established by the First Progenitor and tells Urd to leave Japan. Urd questions him and says Saitō is no longer a vampire. Saitō reveals he worked with humans before leaving. Urd wonders if Saitō is bored of living. Saito targets Urd's aircraft with a large scale missile attack.As they are both Second Progenitors, Urd and Rigr have known each other for centuries and have become incredibly familiar with each other desires and motivations,as seen when Urd was able easily see through Rigr's intentions of wanting to meet up with the First Progenitor and managed to guess accurately on his true desire to simply obtain the First's attention, causing both pity and anger from Urd due to him having long having realized the First's complete disinterest in the rest of Vampire Kind and wishes that Rigr would too.
During the flashbacks to Ancient Greece, it is shown that Urd and Rigr had a cordial friendly relationship with each other due to the both of them being the eldest vampires sired by the First. They are seen sharing duties and jobs given to the by the First Progenitor, as when they were both given the duty to teach the newly sired Ashera Tepes about his new abilities and powers as a vampire and the new rules he must follow. The two are seen friendly bantering and arguing with each other in a familiar, friendly way.
During this time, Urd is also seen having been slightly annoyed by Rigr's constant attempts to gain the first's attention in such instances where he worriedly/annoyingly aimed a look at him as he tried to talk to the first.
A vampire noble who works under Saitō's commands, Basteya addresses him as lord Rigr Stafford and reveals that he is the one in control and they just simply play their part. This is evident further when he sided with an agent from the Hyakuya Sect to retreat from the battlefield. Basteya would obey Saitō even if they have to sacrifice themselves to increase his power, going as far as using a spell that would take of their life force at his command.
A vampire noble and Saitō is his master. He sent him to meet with Guren as a guide so that Saitō and Guren could meet. At first Mahiru was hesitant if she and Guren should meet and talk, or fight each other. He obeys Saitō's orders without a question. His orders was to delay Guren's friends until Saitō and Guren are done with their conversation. He stated he understands very little of his goals, and everything he does doesn't make sense to him. He addresses him as Rigr Stafford, but he knew his name as Saitō as well.
Originally a vampire Ashera Tepes, Saitō along with Urd Geales were witnesses when the first progenitor, Sika Madu disappeared with him 1,000 years ago. Sika intentionally turned him into a demon against his sister Krul Tepes wishes which he ignores. He and Urd waited for Ashera to wake up soon after his transformation, Saitō says along with Urd that they will have to teach him control his thirst for blood.