These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Esoteric Happy Ending: Yeah, Karin and Kenta have their happy ending, but, the vampires will likely become extinct because all of the women, sans Calera, are infertile. Then again, Ren has a son by Bridget...
The Woobie: Karin is the black sheep of the family because of her ability to give blood, stay in the sunlight, and eat human food, and thus, she is one of the loneliest vampires. When her little sister Anju becomes a full vampire, she realizes how alone she is and she cries as she makes breakfast for herself.
Also, you can't say you don't feel sorry for her when memories of her family is erased and she thinks of them to be dead after graduation.
Yuriya Tachibana, who is a half-vampire, half-human hybrid. After her father died, her mother struggled to raise her alone, and passed away from the stress. Her first biting victim was someone she loved back in junior high, and, as a result, she was forced to leave town. She is ostracized by the rest of the vampires because a "half-breed" outed the existence of vampires to a human church a hundred years ago, and they were nearly wiped out, and they see her as a threat. Elda almost killed her until Karin intervened, and Bridget is especially nasty to her, calling her an "empty doll" and suggested that Yuriya kill herself, but hasn't yet because she doesn't have the courage to do so. Her Uncle is the only person she can rely on.