|Full Name||Saegusa Kouichi|
|Affiliation||Ten Master Clans (Saegusa)|
|Occupation||Family Head (Saegusa)|
|Novel||Volume 11, The Ojou-sama's Magnificent Day Off|
|Manga||Volume 1, Chapter 5 (Mentioned)|
|Anime||The Irregular at Magic High School The Movie: The Girl Who Calls the Stars|
Unlike the Yotsuba, Kouichi is very close with his children, which Tatsuya noted how shocking it was that Mayumi was able to have family conversations with him. The Saegusa are in the public eye as well. He had two sons with his first wife, and three daughters with his second wife. The older brothers are not close with their younger half-sisters.
In the beginning Kouichi and Maya had a very close relationship, and they loved each other very much. However Maya was kidnapped and he failed to protect her from being taken. Ever since 'The Nightmare of 2062', they had a strained relationship. Maya was violated, rendered unable to have children, and her mind was altered to ease her mental anguish.
Currently Kouichi treats Maya as a rival, and fears that the Yotsuba Clan has gained too much power and needs to be weakened.
He was Kouichi's right hand man. He was used as bodyguard for Mayumi, and carried secret missions for Kouichi. The two had only a business-type relationship.
Kouichi has a close relationship with his daughter, Mayumi. Kouichi is able to greatly understand Mayumi's thoughts and feelings, which allows him to know how Mayumi reacts in various situations.
Kouichi has taken an interest in Tatsuya. Currently Kouichi is interested in Tatsuya and wants to meet him and Miyuki in person. He watched as Mayumi prepared a Valentine's Day Chocolate in the Visitor Arc for him.
It is not known if Kouichi was of Juumonji Clan's idea to make Tatsuya join the 10 Master Clans through the Saegusa Clan, by marrying Mayumi or one of the twins (Kasumi or Izumi).
| In Volume 17, Kouichi suspected Tatsuya primarily for his miraculous engineering during Nine Schools Competition, and the strange resurrection during Monolith Code (Regrowth). Later investigations revealed that he has the power to alter the structure of information, and so he could link him with the phenomenon seen in the Scorched Halloween (Decomposition - Material Burst). His suspicion increasing after he found out that Tatsuya is linked with the Independent Magic-Equipped Battalion 101.
Kouichi plans to have Tatsuya marry in the Saegusa Family for two reasons: to weaken the Yotsuba and to gain the skills and talents of Tatsuya in his family, that have drawn attention. Therefore he proposes a compromise between Tatsuya and Mayumi, which was disapproved by his daughters.
However, Kouichi got a chance to see to it that Tatsuya can be seduced by Mayumi as there may be a possible compromise between her and Tatsuya.
Kouichi also has taken an interest in Miyuki due to her incredible performance at Nine School Competition.
|In Volume 17, it is revealed that Kouichi had suspected that Miyuki was a member of the Yotsuba clan, due to her enormous power for to use Inferno and Niflheim easily, and later by incident in Yokohama and the strange power to exterminate others (Cocytus).|