Dekichatta Shitsuji by Mikage Tsubaki

Summary

Plot: Konno Wataru, an only son who is rich, studious, and quite prideful, has a “butler”. In charge of him is the domineering sadist Azuma, holding an official caretaker license and to top it all off, he’s perverted (?!) Amidst their instinct of a cat-dog relationship, things get a bit risqué. —During which, Wataru’s older sister’s baby, Momoka, suddenly appears! With a MIA father, Momoka’s care is left in their hands! In between the teasing, puzzled Wataru unexpectedly witnesses Azuma’s sincerity …however…?!