The BLCD was kinda boring. But the story has a really nice flow. For me there's is no plot holes. Rei was half human and half batsu, and no one even the narrator (mangaka) didn't know about how the half/half gonna work. I think mangaka making it ambiguous to appeal more readers. The reader can imagine as much as they want for this beautiful couple. As for me, the ending was obvious, It's gonna be a very very sad ending for theo but as the time's goes theo will eventually let it go. The feeling will linger forever but as time goes by, theo will not gonna sad again as much as the day rei died. As for rei, he will have a satisfying life, he spends his time with his lover and trying to make a more happy memory. They really beautiful.
THEO