I didn't know that Overlord Lover was the name of a novel, nor did I know if there was an animation. If you can provide more information or context, I will try my best to answer your questions.
There are many excellent anime like the younger sister and lover. Here are some:
1. Index of Forbidden Magic Books
2 "Battle of the Date"
3."Gentle Girl"
4." Science's Super Electromagnetic Cannon "
5. Sword and Sword God Domain
Dragon and Tiger
7 "Even a chuunibyou needs to fall in love!"
8 Naruto
9 " The Attacking Giant "
Ghost Blade
Of course, this was just a list of some of the other excellent animes that could be chosen according to one's preferences.
This kind of story can be complex. In some cases, it might involve issues of interracial relationships and the challenges they face. For example, the couple may encounter cultural differences. The pregnant woman might have to deal with different family expectations from both sides. Sometimes, society's perception can also play a role, either being accepting or having some biases.
The 'Black Bull Lover Story' might be a local folktale. It could involve a young shepherd who falls in love with a black bull in a sense of deep admiration for its strength and beauty. Maybe the bull has some magical qualities that attract the main character, and they go on adventures together in the fields and meadows.
In some possible versions of the 'Black Bull Lover Story', there could be a group of villagers as well. They might not understand the special relationship between the lover and the black bull at first. So the main characters could include the lover, the black bull, and the skeptical or curious villagers.
Love and acceptance. The idea of a human or another being loving a black dragon goes against common prejudices in the fictional worlds, so acceptance is a big theme.
This is a rather complex and often uncomfortable topic. However, one could imagine a story where a wife in a racially diverse community befriends a black man through common interests like community work. They develop a deep platonic friendship which is misconstrued by others as an inappropriate relationship. But in reality, they are just good friends supporting each other in a multi - cultural environment.
Because I am a person who likes reading novels, I don't have the ability to browse the web. I could only answer what had happened or what I had learned.