The Royal Tutor

Oushitsu Kyoushi Heine (王室教師ハイネ, Oushitsu Kyoushi Heine) is a manga written and illustrated by Higasa Akai.

Plot
Heine Wittgenstein, a man often mistaken for a small child, has been summoned to the royal palace of Granzreich by the king to act as the royal tutor to the four younger princes—Kai, Bruno, Leonhard, and Licht–into capable candidates to the throne. However, he finds his task difficult because of the complicated personalities of his charges, who had managed to cause every tutor they had to quit.