Ishikawa-sensei is a supporting character who serves as a teacher at Doumori Elementary School in Hell Teacher: Jigoku Sensei Nube. He is most frequently seen among the fifth-grade teaching staff, and it is widely believed that he functions as the physical education instructor for that grade, though this is never officially confirmed. He is a middle-aged man with a notably unkempt appearance, characterized by disheveled hair, a beard, and glasses. His typical attire is a jumpsuit, which he wears almost constantly during his time at the school. This scruffy and casual look sets him apart from the other faculty members and contributes to his somewhat unconventional presence in the story.

In terms of personality, Ishikawa-sensei is a peculiar individual with a mix of both helpful and questionable traits. On one hand, he occasionally offers useful advice and shares spiritual knowledge that he has gathered from his own life experiences, demonstrating that he possesses some awareness of the supernatural world that surrounds the school. On the other hand, he has a number of dubious personal habits that reveal a less admirable side. He is known to avoid bathing for extended periods, sometimes going over a month without showering. He also keeps cards for adult shops hidden in his jumpsuit, a fact that is accidentally discovered by the protagonist, Meisuke Nueno, when they fall out of a borrowed suit. Additionally, he has a fetish for wearing women's undergarments, which once played a role in a plot involving a demon from hell. These aspects of his character present him as a somewhat shady and irresponsible figure, making him a source of comic relief within the series.

His motivations are not deeply explored, as he is a minor character whose primary function is to add color to the school setting. He does not drive the plot forward nor does he have any grand personal ambitions. Instead, he exists as a familiar face within the faculty, occasionally interacting with the main characters in ways that highlight either his obscure knowledge or his eccentric flaws. His role in the story is largely that of a background staff member who becomes briefly relevant when his unusual behaviors or possessions intersect with the supernatural events that Nube must resolve.

Key relationships for Ishikawa-sensei are limited. He is a colleague of the main character, Meisuke Nueno, and is shown interacting with him on several occasions, often in moments where Nube becomes entangled in the consequences of Ishikawa-sensei's habits. He also appears alongside the other fifth-grade teachers, suggesting a casual working relationship with them, but no deep bonds or rivalries are depicted. His connections are strictly professional and superficial.

Ishikawa-sensei undergoes a notable change in the epilogue and sequel series of the story. After many years, he is promoted to the position of principal of Doumori Elementary. With this promotion comes a significant transformation in his personal appearance. He begins to dress more neatly and tidies his previously messy hair and beard, resulting in a look that somewhat resembles the former principal. This development indicates a degree of character growth and a move toward responsibility, though his earlier eccentricities remain a memorable part of his legacy. As for notable abilities, Ishikawa-sensei does not possess any supernatural powers or combat skills. His only standout traits are his practical knowledge of spiritual matters, gleaned from personal experience, and his distinctive ability to inadvertently cause awkward or comedic situations due to his unusual lifestyle choices.