Blood Alone, Inu x Boku SS Recommendations
Both have a younger female being protected by an older male, as well as elements of the supernatural. In Inu X Boku it's youkai, in Blood Alone its yampires. Both a sweet and have great characters and an interesting story.
They involve a different type of species but both series shares a familiarity between the main characters' relationships. Their chemistry develops throughout the story as we see they learn more about each other. And despite some of their differences, the main characters begins to appreciate each others' company and even seemingly have a bit of romance between them. Both series also adapts supernatural elements involving other species. Inu x Boku SS is more well known for its comedy gags while Blood Alone contains some more mature context especially in later chapters.