Class 1st-year Ha-class Committee Explosives Occupation Theory teacher, Advisor A skilled and good-natured teacher, Doi is both strict and kind to his students. Despite his frequent stress-induced stomachaches caused by his class' poor academic standing, Doi remains persistent in trying to teach them, and believes in their practical abilities and individual talents. He is well-loved by his class, as well as the other nintama and staff of the Ninjutsu Academy. Outside of his job as a teacher, Doi works proficiently as a ninja. However, he is also shown frequently forgetting to pay his rent or attend town cleaning due to his busy life preparing make-up classes for the 1st-year Ha-class. He also shows a rather childish side when faced with his least favorite food. Doi is of average build and height, with a slight baby-face. He has upturned eyes, a slightly pointed nose, and defined eyebrows. Notably, he has long, messy brown hair, but this is completely hidden when he wears his current ninja zukin or his casual hat, giving the illusion of short hair - usually, all that is visible is his characteristic bangs. In the past, this hair was tied in a messy ponytail.

Spoiler

Doi-sensei was brainwashed by Dokutake in the novel "Rakudai Ninja Rantarou: Dokutake Strongest Warrior," and had another persona known as Tenki. He eventually recovered his recollection and returned to his student.