The Servant Prince

Naoya has always been the top dog in school. The son of a CEO, he excels in both his studies and sports. Conversely, Takaaki has always been at the bottom of the totem pole, an introvert and Naoya's errand boy, obedient to his every command. So much so that he even licked Naoya's feet when ordered. Years later, their positions are reversed: Naoya has failed at running his company and is now unemployed, while Takaaki has become the president of a successful startup. Yet upon their reunion, Takaaki continues to serve Naoya with the same blind devotion?!

(Source: MangaPlaza)