I can't come up with a proper answer. It's kinda contradictory, between love and hate relationships about this one.
I like the fact that the term "thirst for blood" is presented as a disease. There is no connection with vampires and so on. But, that is not the whole subject of the problem. This tells a pair of sister and brother who are locked up in their nests with mysterious diseases.
You don't get anything other than those that are in the spotlight, even the information behind them is pressed as little as possible. The dark and miserable side can be described beautifully without being too melodramatic.
I really like the element of romance here. It's painful and tragic. I don't know if this is a subjective impression because of my taste, there is a something different about Chizuna and Kizuna’s relationship. I understand that they are sister and brother, they need each other but there is no connection with incest, it is different. I hope that they stick with the concept to the end and they did, but at the same time they did not. There is a limit between them.
Everything going well until a nurse appeared as a third party. This is one thing I did not expect, "there are outsiders who put their noses in other people's family affairs". I don't like it. It feels like rushing to the end of the story and provide a lot of information in a short time. Imagine if there were outsiders who dared to investigate without permission with the reason "because he decided to commit suicide suddenly, so I want to knwo". For god’s sake, that's about privacy.
Why doesn't the author just let their aunt/uncle to take the action? They are acquaintances of Chizuna and Kizuna's father. Don't you think it's weird? The author must keep the concept “only everyone involved to know”.
The part I like the most is some chapter towards the final. There is an atmosphere of relief and free from restraints. Some of the scenes where Chizuna could laugh out seemed to show the seconds before her death. She has a big role here, who always sacrifices, she deserves to be happy.
And regarding the conclusions, it was not satisfying.
Kizuna forgot his memory and the case were closed. How and why it comes to this, author? I left hanged.
If I'm the author I will not choose that option. You know, this is broadly about dependency and emotional bonding with others. The trigger is an emotion that cannot be separated from the past. It doesn't need to be debated scientifically, medicine and so on, but how to cure and fill the gaps between the two. Everything is the matters of psychological.