Great Teacher Onizuka, Mob Psycho 100 Recommendations
Reigen Arataka and Onizuka are highly similar in character: People who at first glance, would seem like swindlers or frauds. More than that, what makes them similar is, they genuinely care for their sidekicks/students and are ready to protect them from any harm that they may encounter.
Imo, both Reigen's design, as well as character, is heavily inspired by Onizuka. Both also possess that subtle charisma and self-confidence that makes viewers like them.
-Both has main characters who are damn funny Onizuka and Reigen, Arataka
and both shows consist of comedy and have someone who wants to protect others.
Combine Reigen Arataka's cunning and character design with Mob's "saving the day," and you get Eikichi Onizuka. GTO also has a similar master-apprentice vibe. I recommend watching it.