All three are clones of their ancestor. The twins are clones of the human who saved the siren god (Chen Yuan), the second human that Chen Yuan bound to after being betrayed. Mercury is the clone of Chen Yuan.

OE and almost leaning toward BE.

Tang Yi and Mercury are literally separated for 8 long years with Mercury thinking TY is dead. TY doesn't want Mercury to see him because he doesn't want to burden Mercury as (yes, it gets worse...) he has cancer from radiation exposure and is very sick. Mercury only finally gets to see him at the last chapter and it just ends with them meeting. I'm so devasted that that's what readers get after they suffer sooo much their whole lives. It feels unjust. I get that in this bleak world, this is probably a realistic ending but I'm not satisfied by this ending. I just wish I never read the ending. TY and Mercury deserve so much more. I just want them to live well and I want to have a glimpse of their relationship without the wars that they've lived through. Funnily enough, it seems that their best relationship moments are well before the ending. The ending makes me feel like I lost something. I thought that with such a dark, depressing setting, that the ending was bound to be better for the MC and ML and it's not. I'm bitter about how TY and Mercury, for most of the story and what we know of their lives, live for others and live in a plot that's planned out by others (like literally they're just chess pieces in the grand schemes of those in higher positions than them. They just get thrown around left and right, falling into every single trap/path that was pre-planned for them.) And in the end, we see that they still live for others. When they meet in the end, it's implied that they will live for themselves but I want to see that. TY isn't expected to live long and is far from his strong, healthy self, while Mercury will live for hundreds of years. Some part of me wants to believe that Mercury is able to heal him and they are able to spend many wonderful years together.

The fate of Tang Ya is just so sad as well. And Liu Huo and Jang Yanfeng dying together in the blast. I wish we got more about the rest of the lives of the 15th squad as it seems like everyone mostly separates to do their own thing.

cleanse this sad, bitter, devastated feeling.

regarding the squad, I honestly didn't expect the sirens and their partners to get rid of their bond in the end. But then, looking back in the plot, it was understandable because the bond in the beginning was "fake" due to the brainwashing program. But they stayed in contact and it's implied most pairs are still in a relationship despite the distance. So the ending was almost bittersweet for all the relationships yet hopeful in the apocalypse setting. Also agree that MC and ML's ending was HFN and the most bittersweet. Their happiness and brief respite begins only at the end of the book and it seems to only a short moment. But author's note wrote that author finally wrote a HEA (does this mean author's other works are all BE?) so I guess this is the best ending we can expect already.

I just totally felt sad when Jiang YanFeng sacrificed himself. His unrequited love story was one of the strongest emotional points of the story for me even though it was like 1 chapter only.

the siblings affection in this one hits hard I cried so hard when reading abt tang ya's sacrifice for tang yi more so than the angst between tang yi and mercury and then Jian YanFeng??? I was shouting bloody mu*der reading that one chapter

Inferno and Jiang yangfeng tho. I cried because of them first. Then Tang ya. He adores his little brother. Finally Tang Yi. He will probably die in a few years and idk how will Mercury cope with that.