Nagisa is a petite-framed boy with blue hair and azure eyes. His hair goes past his shoulders due to his mother forcing him to keep it that way. He kept it in a long ponytail until Kaede Kayano joined the classroom and styled it in two pigtails.
Nagisa is a calm, collected, and friendly individual who can be exceptionally observant and circumspect of his surroundings and the situations that develop around him. He tends to pay strict attention to Korosensei.