I'm just sad that Satoru and Saki end up together...
yes it makes sense that they are together because the other 3 are dead meat, but still, it saddens me
and there are still a quite amount of open end questions left by Author and I will just share my view to those.
Shun is alive or not?
For Shun, some people are saying Saki is just having an unstable mind and Shun is just an illusion because from the end of the novel, Saki mentioned that she havent seen Shun in her mind after she turned 35. Still, nobody ever found Shun's corpse so it is an open end question of whether Shun is alive or not.
How Maria and Mamoru die?
The novel also didnt explain how Maria and Mamoru exactly died, I would guess that Maria is very weak after pregnant so she died when she gave birth. As for Mamoru, his body should be very weak after escaping for such a long time and eventually he died.
The 'truth' medicine dinner:
According to the novel, one of the child's dinner has some ingredients or medical that will make the eater tells the truth... It is uncertain that who eats it... I'm guessing Saki since she is the narrator and she is the weakest in terms of power at that time...
Satoru's love relationship:
I still believe that Satoru only loves Shun, yes people are saying after he turned 26 he has some feelings towards Saki but IMO those are not love. They go for each other because they both love Shun and use each other as substitute. and then just let things naturally flows into a married couple. (but im biased towards yaoi)
Maria:
As for Maria, I still think she likes Saki as her letter suggests: I love Saki from the bottom of my heart, but only me can protect Mamoru and I cannot leave him alone. In the other hand, people could also argue they have a child so they must love each other, but since they still need to control their power I think sex is unavoidable.
Shun:
Even though I like yaoi so much, but I think Shun loves Saki more. He says goodbye to Saki when he about to turn into a devil. and also he did confess to Saki when he 'died'.
So overall, the luckiest person is Satoru as he did dated Shun, Rei and Saki. Lucky him!