This was a decent effort at a supernatural horror, though I wish we got more scenes between Tenshuu and Gondou, to flesh both of them out. I dislike the trope of pitting two unsympathetic characters against each other, only to reveal that one of them was justified in what he did, or had been sympathetic all along. Though I suppose there were hints of this before, with the prison warden saluting Tenshuu through tears as he was led away.
Plus, the whole "I killed them because they raped my girlfriend" premise is tired at this point; I'd much rather have had Tenshuu just...kill those people, or not have received any explanation about his past at all except "he killed 4 people and his girlfriend". Let the reader decide whether he's sympathetic or not solely based on the present events.
But I will say that I liked the hallucination flashback with his idea of Misako blaming him for being distant and for doing something she never actually wanted. These avenge-my-woman plots always have a vibe of "you messed with my property, now you have to pay", and I'm glad it was somewhat called out here. It's understandable how Misako could've simply needed him to be there for her, and interpreted his emotional distance as a rejection (which, for all we know, could've been true, and not just Tenshuu's guilty thoughts).
By comparison, Gondou gets none of that depth. He's just an unlikable cardboard cutout and wasted opportunity.
If I could take out some details to leave room for everything else, I'd take out the female scientist entirely. Her presence isn't actually that necessary, and she could've been replaced with Kojima (just say he was obsessed with Yurika, or with getting the Black Entity for himself). Seems like a lot of time and space were spent on the sister, and it took away from what could've been character development. As-is, no one actually develops at all, they stay exactly as they were introduced.
The Black Entity premise reminds me of Poe or Lovecraft stories. Very much "humans fucked with something they should've left alone".
In the end, the difference between a 7 and an 8 is the art. Very enjoyable to look at.
8/10