The story revolves around the core concepts of Life, death and how death of an individual not only makes a physical absence in space & time but also how it creates an emotional void in the lives of people that are affected by it.

Story -
The story is between mediocre and good. It does a fairly decent job in showing how death affects different people in different ways. As the story progresses it might get confusing for some so you have to pay attention when you read and you have to really catch certain hints that the author throws in order for the ending to make sense.

Art -
I usually don't care much about the art because every artist has their own style but the faces of the characters in this manga were very similar. It was very confusing.

Character -
There are so many characters in this story, some are very important and some are totally unnecessary. You won't see any major character development in this story.

Enjoyment -
It does a good job to keep you entertained for a while. It's not lengthy at all so you can read the entire thing in a day or over the weekend. It can be a good substitute for a short mystery novel. It's not crazy good but it's not boring either.

Overall ( S P O I L E R S I N C L U D E D ) -

Now this is how I see it, the triplets were not triplets but in fact the same person. I don't understand how some people don't get this detail but it's pretty clear.
Tachibana was an immortal being. Every time he died, he resurrected. If I remember correctly he mentions that he even tried to take his own life but it didn't work and that this was an endless cycle for him. He also mentions that it has gotten to the point where any physical misfortune is treated as a mere cold. I think this is the reason why he works in the cleaning industry so that he understands death a little more as he himself is immortal.

He meets people like Taji, Omi Katou and Yanazame and gets attached to everyone at AUN. When Taji introduces Masato to Tachibana, Masato freaks out. Masato asks him about tachibana's "dreams" but Tachibana indirectly tells him to forget about the whole thing but Masato still ends up murdering Tachibana.

Tachibana again resurrects and this time ends up at Taji's place wearing a mask. There he asks Masato to stop again. I think he does all this because he actually cares about Taji and does not want him to get hurt. Tachibana also does this in order to take up the identity of END so that Masato's name comes out clear and so that he doesn't end up being a suspect. Masato, yet again, does not realise this and finds Tachibana and murders him and keeps on playing the END's role.

Tachibana then AGAIN resurrects and later informs the police about END and disappears. Tachibana who himself is immortal sees death of people around him, who are close to him and puts this whole ordeal to an "END" by murdering Ezaki who was directly responsible for the suicide of all the END Victims and the suicide of Omi who was close to everyone at AUN including Tachibana.

This could have been a really good manga but the author fails to make a good transition from it being a thriller/mystery to supernatural thriller/ mystery. It gets confusing for most of the readers.