Naoi is a boy with chin-length dark green hair with fringes swept slightly to the right. He wears the default uniform of the afterlife school which consists of black pants and a white polo shirt worn under a black gakuran (he is the only SSS member in the Anti-Angel Headquarters that doesn't wear the standard 3S uniform). He also wears a variation of a Mao cap, with a dominant dark blue and black color scheme. Whenever he goes on his rounds on the school's classes, he is usually flanked by a small group of students, particularly NPCs.
Before joining the SSS, he is much stricter than Angel was and his first action as president is to punish the SSS for their constant disobedience. He even massacred the SSS after Otonashi and Kanade were sent to the reflection room. Later on, when he joins the SSS, his affection for Otonashi and antagonistic attitude towards the others are used as a constant source of comic relief. He often says negative remarks on others, and then says that with the exception of Otonashi. He also claims himself that he is a God, though the SSS insist that he is not. His victim on hypnotism is mostly Hinata, mainly because Hinata always pick on him.
In his living years, Naoi is one of the twin sons of a man famous in the field of pottery. His brother inherits his father's skills in making pottery, while he is left alone in the house usually playing alone. In an accident, he and his brother fell off a cliff and his brother perishes from the fall. Upon his recovery, he made the decision of his life: to replace his departed brother by switching sides with him, telling his father that he is his brother and that he was the one who died in the accident. Upon his recovery period, he undergoes a strict training from his father to assumingly bring him back to his skills in pottery, which in fact, he did not possess in the first place. He did his best efforts and manages to receive awards, though not in the same league as his award-winning brother. Soon, his father was diagnosed with a terminal illness and was bedridden. Not being able to continue his training, he nurses his dying father as his family's name slowly sank into anonymity.
When in combat, Naoi uses a pair of Heckler & Koch USP pistols but his main ability still lies with his remarkable hypnotic abilities and his high intelligence. From the banter between Yuri and Naoi, both are close to the same level of intellect.
- Naoi bears a striking resemblance to Naoto Shirogane from the game Shin Megami Tensei: Persona 4.
- His hypnotic abilities resembles the geass Lelouch uses in Code Geass.
- He is the only SSS member in the Anti-angel Headquarters not to wear the 3S standard uniform.
- In Episode 8 Dancer in the Dark, when everyone sacrifices themselves one by one to stop Angel's clones, he is the only character to not have his name cried out when he is killed by a clone, to which Yui said she did not know his name.
- During the OVA Stairway to Heaven, he is nearly run over by Hinata and Noda during the dust-cloth race, in which he comments if they were trying to kill someone. Otonashi apologizes with the end comment "they have always acted like this".