Heine is a close friend of Viktor's. He cares about his well being and dislikes when Viktor makes jokes about him being a child. When Viktor was shot by a guard in their younger days, Heine tried to fight off all the guards until Viktor told him to stop. After Heine stopped, he was imprisoned and was accused of trying to assassinate the prince, Viktor. While in prison, he was praying that Viktor would stay alive, and he was happy to see him alive and well when Viktor came to get him out of prison.
Leonhard didn't want a royal tutor believing that they are evil, and he disliked studying. When he was interviewed by Heine, he wanted to run away due to the fact that he had to take a test. Realizing that Heine found his journal, he was embarrased and tried to take it from him. After finishing the test, he was thinking that Heine might be different because he didn't laugh when he read his journal. Because he wants to be praised by Heine, he studies more and more and tries to catch up with his siblings. He pretends like he doesn't like Heine.
When Bruno first met Heine, he thought that he was not needed due to the fact that Heine never went to college and believed that Heine couldn't teach him anything else. However, that view changed when he tested Heine in various subjects (ex: chess, solving arithmetics, playing instruments, etc). Bruno respects Heine like a master due to seeing his brilliance, and he refers to Heine as "master". He considers himself as an apprentice of Heine too.
At first, Licht was okay with having a royal tutor. Since most of his brothers didn't want to have a tutor he went with whatever they said. During the interview with Heine, he was asking obscene questions that provoked Heine. After the interview was finished, Heine felt that Licht was the most suspicious of all the princes and believes that he should be cautious. Later, he discovered that Licht was just an ordinary person to him.
Heine thought that Kai would be the most troublesome out of all the princes due to the "glare" Kai gave him. Heine discovered that Kai was the opposite of what secondary sources said. Kai likes being with the professor because he was the first tutor that he got along with. Another reason Kai likes being with the professor is because he is small, and his hands are soft.