|Occupation||Clerk in MBI's pharmaceutical department|
Natsuo is a normal-sized young gentleman with brown hair, wearing throughout the entire story an elaborate suit with a white shirt underneath and a black tie. His hair is white in the manga.
He seems to be very easy going about the whole Sekirei Plan and appears to judge fights between Sekirei as nothing more than to have fun. He appears to not care much about his Sekirei's general well-being and carefreely admitted they often complain about this side of him, which clearly becomes visible when he spills out secret information in his conversation with Minato about Sekirei extermination.
Natsuo harbors hatred for the world as in his eyes it took his lover away from him. It is perhaps because of this hatred that he was able to wing Karasuba, as it may have given the two something in common.
- No. 04 Karasuba (Nicknamed: The Black Sekirei)
- No. 104 Haihane (Nicknamed: The Blue Sekirei)
- No. 105 Benitsubasa (Nicknamed: The Red Sekirei)
Not much is known about his history except that he works as a clerk for MBI. In the past, Natsuo was in a relationship with a doctor serving in a war zone. At the time his lover perished, Karasuba approached him. During a conversation, Natsuo stated he was angry at the world that took his lover away. Karasuba related to this through her relationship and unsettled rivalry with Yume and was angry that she sacrificed her life to save Musubi. She later chose Natsuo as her Ashikabi so they can "destroy" the world that they hate.
Natsuo makes his first appearance when he drives Karasuba to Izumo Inn. After Karasuba's visit he also drives her home stating that he know that she is happy just because he would be her Ashikabi. The next appearance of Natsuo is during the escape plan. He is shown in the MBI tower baths discussing the escape attempt of Minato's party with Karasuba. He assumes that something interesting will happen and Karasuba states that Natsuos intuition never were wrong. The next time Natsuo appears is in the third stage, third battle ordered ther by the president to participate. He nearly got buried under all the rubble when Musubi destroyed the junction but got rescued by Haihane.
Shortly after Minato was dropped by accident near Natsuo a conversation between the two started. Minato is surprised recognizing who is in front of him but Natsuo calmly introduces himself as a clerk of MBI's pharmaceutical department and the leader of the Disciplinary Squad. He then tells Minato to be careful cause it would be bad if the Sekirei see an Ashikabi alone. He tells Minato that even so it is strictly forbidden for Sekirei to attack Ashikabi there would be Sekirei in the Disciplinary Squad who don't follow this rule. He then asks why Minato hasn't heard of any Ashikabi dying yet and what would happen if an Ashikabi dies. The answer to this question shocked Minato cause Natsuo informs Minato, that all Sekirei an Ashikabi has winged would get terminated.
He then says that if they wouldn't have a trick as such it would be hard to control the Sekirei. It would be just like Sekirei are, MBI hasn't anything to do with this. During the conversation a Sekirei of him, Haihane, was engaged in battle and got hurt. So he offered her to use the Norito. But because of this Oriha, Haihanes opponent noticed Minato and Natsu and started to attack them. Haihane interfered to rescue Natsuo and got serious attacking Oriha blasting her away. In the last minute a blade from Orihas attack was deflected by Tsukiumi which otherwise would have hit Minato. While Haihane and Tsukiume are fighting Natsuo continues his conversation with Minato like nothing had happened. He is asking Minato why he thinks he is telling him such information and assumes Minato is just thinking he would be careless like his Sekirei do. He then asks Minato why he doesn't kill him cause if he would do so the complete Disciplinary Squad would be annihilated. While Minato wonders why Natsuo would tell him something like that Homura pulls him forcefully away interrupting their conversation.
Natsuo then is seen to watch the fight between his and Minato's Sekirei, noticing that they are at a disadvantage and thus offering them to use the Norito. Before he could kiss his Sekirei a phone call from the MBI president interrupts and they retreat from the battlefield
Natsuo appeared along with Benitsubasa and Haihane to retrieve Uzume's body (a job his superior Sahashi Takami usually is responsible for but due to her commitment to treat Chiho's disease she's unavailable) after she was killed by Sai, one of Higa's Sekireis. He convinced Minato to give Uzume's body to them in which Minato refused to give at first, but after saying that Uzume's body is still alive, Minato gave the body to them and soon went out without any fights ensuing.
- Out of his three Sekirei, only Benitsubasa is shown to have genuine romantic feelings for him, although Haihane grows to care for him as well.
- Natsuo has a much darker side that only Karasuba knows. He wishes to destroy the world, which drew the Black Sekirei to him and they partnered as their goals are the same.
- If a Sekirei does draw power from love, that explains why even with Natsuo's Norito power up, the Black Sekirei struggled to beat Kaho: Natsuo has lost the capacity for love and said to the Black Sekirei (about love), "Because...you and I are hollow." Kaho, meanwhile, was full of love from her Ashikabi, as because of him she was able to become strong and self-actualized as a person. Furthermore, love is vital to Sekirei in general, regardless of whether or not they're fighting and using it to power up.
- Sekirei Manga chapter 91
- Sekirei Manga chapter 109.5 omake
- Sekirei Manga chapter 17
- Sekirei Manga chapter 19
- Sekirei Manga chapter 41
- Sekirei Manga chapter 85
- Sekirei Manga chapter 88
- Sekirei Manga chapter 89
- Sekirei Manga chapter 90
- Sekirei Manga chapter 92
- Sekirei Manga chapter 93
- Sekirei Manga chapter 109