Leonhard von Granzreich (Leonhard von Glanzreich in the Crunchyroll subs) is the fourth prince of the Kingdom of Granzreich.
Leonhard is a young man with short blond hair and, like the rest of his family, he has blue eyes. In Heine's information about the prince, it is said that Leonhard is the most beautiful boy in the Granzreich kingdom. He is always seen dressed neatly and formally, even though he is in the palace and not in the presence of his father, Viktor von Granzreich.
From first impressions, Leonhard seems to be a haughty, vain young man who looks down on commoners. In reality, he's actually very socially awkward and constantly beating himself up for small issues. Despite not being the youngest brother, he's the most childish due to his petty jealousy, being picky with food, naivety, and tendency to pout and cry whenever something goes wrong. He's also prone to giving up easily and running away from his problems.
However, Leonhard can also apply himself given the right encouragement, and has a strong sense of justice. His simple way of thinking allows him to look at problems more easily. He shows a more serious side when it comes to athletics, which he excels at. He acts as a tsundere, someone who pretends to be mean but in fact desires to be loved and particularly enjoys being praised. Because of his simplistic mind, it is relatively easy to trick and manipulate him. He is a crybaby and often complains but has over time grown and has tried to work harder to be king. He is very honest, tending to say blunt or rude comments without thinking how they would hurt someone and also being an extremely bad liar, as he wears his heart on his sleeve.
Out of all the princes, he appears to be the least likely to be able to survive on his own or if he were a commoner, not having studied nearly his whole life, not even knowing the concept of money and not understanding certain commoner things such as eating with hands or having picnics without tables. Heine once pointed out he would not survive if he were not royalty. He becomes attached to Heine, as he treats him well (especially since his other teachers were abusive) and became jealous upon learning he had other students and feels as if Heine only works for him because he is compensated, but Heine assures him that he has never had a student like Leonhard (given his horrible grades) but is thankful for being his tutor and helping him grow to be a better man.
As a child, he was never good at studying, and his first tutor was very strict with him, even using the rod on him. This has caused Leonhard to hate all teachers and to run away from things he detest, he was never caught until Heine arrived.
Leonhard first appears with his brothers, waiting for Heine to arrive. He seems to greet him in a friendly manner before dropping the act to show his disgust towards tutors. He refuses to acknowledge Heine as a tutor, but he completely ignores him and proceeds to ask who would be interviewed first.
However, Heine was understanding and helped him. They slowly get accustomed to each other and Leonhard finally acknowledges Heine as his teacher.