It was confusing at first but as the story went on everything became clear. In my understanding their past life never had the closure since I think it was a sudden death so after the reincarnation their souls splits, half from the past and half from the present. The past started to haunt seme and uke. It started from dreams until one day seme was complete defeated by the past self.
I like the part where uke was begging while crying to bring back Yahiro. It actually made me bawl with tears. I love how the closure was made... Letting go of the past definitely is the hardest thing to do. Fortunately, the past selves were able to meet and accept that they are the past.
Although I want to say that the present them falling in love was kind of baffling because we all know that originally they are straight– but I guess being in that position where you're emotions are being affected by something like the past, it would definitely change your feelings as well.
Over all, the story was melancholic... It pierced through my heart. Made me think about the hardships of the past where bomb fall like rain. Although everything work out for the better, I still feel bad for their past selves because they died early. Kinda regretful but also happy because no one was left behind to suffer for many years.