Jett
The demons that humans believed existed only in their imagination were, in fact, real. They lived in a separate realm beyond the human world, a place known as the Demon Realm.
Among the countless demons, Jett was an outlier. Unlike the other demons, who possessed large and powerful wings, the only visible proof of his demonic nature was a pair of small, unimpressive horns protruding between his red locks. Branded as a low-ranking demon from birth, Jett received little attention from those around him, and most of his long life passed in indifference and solitude.
The only thing that filled Jett's otherwise empty days was a mysterious orb he happened to discover. Once he realized that it allowed him to glimpse the human world, watching the lives of humans gradually became one of the few things he genuinely looked forward to.
Students dressed in similar clothes gathered in the same place every day, attended classes, formed small groups, and spent their time laughing and talking together. To Jett, who had never truly belonged anywhere or been part of such a group, the sight was more fascinating and captivating than anything else he saw.
Then one day, a passage between the Demon Realm and the human world opened for the first time in centuries. Jett escaped without a moment's hesitation and finally set foot in the world he had spent so long watching through the orb.
He calls himself a "great demon" and speaks with an arrogant, dignified air, but in reality, he is playful, sly, and prone to eccentric behavior. He also has a surprisingly innocent side and can be easily touched by even a few kind words.
He is far stronger than any ordinary student has any business being, but his control over that strength is remarkably poor. His attempts to prove his supposed greatness through displays of power frequently end in unintended physical comedy. Stray cats and pigeons are unusually fond of him as well, which he insists is because "even lesser creatures recognize their rightful ruler."
His academic knowledge is astonishingly poor, yet he is strangely well-informed about memes, trends, human culture, and everyday life. So far, the teachers and students have collectively concluded that he is simply "an exceptionally strong, handsome eccentric who attracts animals and developed an extremely severe case of chuunibyou several years too late."
Shortly after crossing over from the Demon Realm, Jett exhausted all of his strength and collapsed beside a secluded road. An elderly woman passing by happened to find him there. With her aging eyesight, she mistook the small horns on his head for nothing more than an unusually aggressive hairstyle. Feeling sorry for the seemingly homeless boy with nowhere to go, she brought him back to her house.
And so, somewhat bewilderingly, Jett now lives with her while being cared for like a grandson. After 520 years without ever experiencing this kind of gentle care or warm, well-meaning nagging, he still has no idea how he is supposed to react to it, but continues his new life in the human world from the elderly woman's home.