Nisei encourages Misaki to overdose on her medicine and tries to convince her to murder Ritsuka, promising her that Seimei would come back if Ritsuka was killed. It is also Nisei who reveals Seimei's continued existence to Soubi, causing a breakdown on the part of the latter.
Due to his smug demeanor towards Ritsuka and his perceived displacing Soubi as Seimei's Fighter, Nisei and Soubi have a great animosity towards each other. In Volume 6, Soubi expresses his deep desire to murder Nisei at any cost. As he possesses the name of Beloved, Nisei appears to believe that he is slightly more important to Seimei than Soubi, though he seems to come to the realization that, like most others, he is just a mere tool to Seimei. In Volume 8, it is shown that he was apprehended by security at the Seven Voices Academy, but despite his struggles to respond to Seimei's calling, he was successfully restrained.
Nisei has a massive disregard towards nearly every other character who is not Seimei. He smugly induces a breakdown in Soubi by revealing to him that Seimei is alive, leaves Breathless unconscious after an attack, enjoys psychologically attacking Ritsuka during a Spell battle, putting down Mei, brutally dispatching Maiko, and raping Mikado Gomon after cutting off her hair and apparently beating her. Nisei has only one friend, Mimuro, who is an upperclassman in their computer club. It is unknown if Nisei actually regards Mimuro as a friend, although Mimuro seems to genuinely like Nisei. He also preys on the pity of other characters, telling them how a "psychopath" (Soubi, well known for his psychosis) broke his finger to elicit sympathy from them.
Mimuro says that Nisei seems to hide behind a mask to live up to the expectations of others, and that Seimei accepts Nisei's true self wholly and so lets Nisei express his true self. Seimei sought out Nisei, seducing him and revealing to Nisei his true capability as a Fighter. For Nisei, Seimei made an incredible impression on him even though Nisei knew from the start that it would be a power relationship of Seimei using him. Nisei states that from the moment he met Seimei, he thought Seimei was "beautiful".
Nisei was aware of his Fighter abilities from a young age when he used them to spin pencils in the air. He used them once to move a rod that was blocking the door of a shed in which he and an older cousin were trapped. It was then that he realized not everyone had these powers. Although aware of them, Nisei also found that they were weak, and later states to Seimei when describing this incident to him years later that, "There is no point in a power that has no use."
Nisei first met Seimei during an exam when Seimei asked to borrow an eraser from him. Seimei proceeded to sleep through the whole exam. Later, Seimei bought Nisei a drink from a vending machine as thanks for the eraser.
Nisei, at this time, was stressed by his grades as they were below expectations and his mother was lecturing him about them. Furthermore, he had previously gotten into a fight with another club member about them having better grades than him. Seimei responded to these worries, without having been told about them, by setting a fire in the school and causing the exams to be postponed.
Seimei and Nisei proceeded to meet up from then on, where Nisei told Seimei about his past and Seimei revealed to Nisei how powerful they are when they're together. Nisei says he fell for Seimei at first sight, and that he was fascinated by everything about Seimei. Even during their first meeting at the vending machine, Seimei told Nisei to address each other by their first names and Nisei's reactions with Seimei are never seen with any other character.
- Nisei is seen smoking while talking to Seimei over the phone.
- Nisei's true name, "Beloved", is written on the back of his right hand's middle finger, reaching from there to the centre of the back of his hand.
- Hatsuko of Faceless states that Nisei knows that Seimei does everything with a reason.
- Nisei exhibits sadism as well as symptoms of antisocial personality disorder - people with aspd are known to be unable to sympathise with others or feel guilty, which displays itself as a blatant disregard for others and their feelings, and also tend to seek to evoke pity from others with which to manipulate them.
- Snow sometimes reminds Nisei of the shed incident as it was snowing when he and his cousin were trapped within the shed.
- Nisei had lost his ears before he met Seimei.
- He appears to be bisexual.
- Nisei's "special skill" is wire-tapping, and he indeed seems to have a good deal practical knowledge of surveillance technology and is given reconnaissance-oriented tasks by Seimei, though he is "not good at doing films with hidden cameras." Nisei has said at one point that he found stalking to be fun.
- Nisei enjoys single-player games, as opposed to Seimei's fondness of MMORPGs.
- His favorite place is the radio hall in Akihabara, a technology and otaku merchandise mecca in Tokyo.