My Hero Academia was not the first anime series to introduce the "gruff but caring teacher" character type, but it does provide a prominent example in today's anime world: Shota Aizawa/Eraser Head, the homeroom teacher of the talented but unruly Class 1-A at the U.A. school. Recently, however, a counterpart has risen to rival his fame: Naberius Kalego of Welcome to Demon School, Iruma-kun!'s Babyls.
Kalego is one of Iruma's teachers at Babyls in Season 2, teaching the Abnormal Class despite his great dislike of troublemakers and misfits. Kalego seems miserable at first, but deep down, he is pleased with his students' progress. He wishes them all well, he just won't admit it, and this makes him Aizawa's equal in more than one way.
How Kalego & Aizawa Became Teachers At Their Own Schools
One of several notable parallels between Kalego and Eraser Head is that they are not only teachers, but former students at their respective schools, Babyls and U.A. Flashbacks make it clear that Kalego was once a high-strung and competitive student before he became a teacher at Babyls, and the My Hero Academia Vigilantes spinoff manga dives deep into Eraser Head's student life at U.A. In his youth, Eraser Head suffered some insecurities about his Erasure Quirk, but he had friends and teachers to support him in figuring out his own tricky combat style to become a worthy hero after all. Years later, his friend Midnight talked him into becoming a teacher at U.A. and he took her advice. Currently, he is Class 1-A's homeroom teacher, despite his own reservations about this arrangement, and he is exactly what the rowdy, powerful class needs.
Similarly, in Welcome to Demon School, Naberius Kalego ended up teaching the Abnormal Class despite his misgivings, and although progress is slow, he is exactly the stern and well-meaning teacher that the misfits in that class need -- from the goofy Valac Clara to the rather pervy Caim Kamui. In both series, both teachers seem unfit to be instructors at first because they are rather self-absorbed and have little charisma, but the reality is that their grim personalities are the perfect foil to the rambunctious classes that they teach.
Bit by bit, Kalego is making an impression on the Abnormal Class in Season 2 of Welcome to Demon School, and more importantly, they are making an impression on him. Kalego may be gruff and humorless, but he is not cruel and certainly not pessimistic. He sincerely believes that each of his students has potential and nothing gives him greater pleasure than seeing them realize that potential. He is tough but fair and will bring out the best in his students one scowl and "Silence!" at a time. In the end, Kalego is a professional who knows his duty, despite his personal distaste for troublemakers.
How Kalego & Aizawa Play Off Of Other Major Characters
Not only are Kelego and Eraser Head similar in personality and roles in their respective stories, but they also have similar relationships with their students and fellow staff members. Each of them has an upbeat and fun-loving adult character to serve as their foil, with this other character exasperating the cool-headed teacher whom they know. In Eraser Head's case, he contrasts sharply with his old friend Midnight, who is well-known for her fun-loving and energetic ways, as well as his old classmate Present Mic, from time to time. Aizawa might roll his eyes a bit at their antics, but he respects them deeply, and the feeling is mutual. Kalego, meanwhile, plays off of the cheerful and doting Sullivan, who ranks higher than him. Kalego must accept the fact that Sullivan will always defend Iruma and dote on him, no matter how much trouble Iruma accidentally causes during the semester.
These teachers are generally distant with their students, but they have found someone to latch onto and nurture, with Hitoshi Shinso being an obvious example for Eraser Head and Iruma the prime example for Kalego, despite the odds. Kalego has many reasons to dislike Iruma, from Iruma's accidental use of a powerful spell during the opening ceremony to Iruma accidentally turning Kalego into his familiar. Despite that, Kalego must realize deep down that Iruma is not a bad person. The boy simply needs some discipline and direction to realize his potential.
In addition, both Eraser Head and Kalego have visited the families of their students to provide updates. During that time, it became abundantly clear that some part of Kalego believes in Iruma and is rooting for him to succeed. And it's not impossible that Iruma might someday become the demon king of Welcome to Demon School; if he does, then Kalego would be wise to invest in Iruma now, getting on his good side before the boy becomes top dog in the demon realm.