It's an alternate universe. Seme's parents found a mysterious mirror that reflects back to us an alternate universe very much like our own that contains copies of us but evil. Anyway, the beings from that evil alternate earth got bored of being evil where everyone was used to evilness. The solution was to create a mirror that could help them escape into a world that was pure and taint it, for them this would be so much more fun! Some of the beings from the evil alternate universe who managed to escape into our world were the Seme's alternate parents. You see, when the alternate beings cross over into our world their alternate counterparts get transported into the evil alternate earth. Eg, if evil you came into our world you would be instantly be transported into theirs. All those exploding people are not dying but are being transported to evil earth! This is why the Seme's parents were so mean, it wasn't really them but the evil alternate selves who had crossed over into our world and were torturing baby Seme! However, some of the evil beings got too greedy and decided to profit off the mirror! They limited the number of evil beings who get to come into out world and those of us who got transported from our world to theres where captured and sold to the highest bidder to be tortured and killed for fun. Some of the evil beings didn't agree with this selctivenes so they made a deal with the Seme and Uke when they were kids as they were locked up in that dark room. In exchange of killing the Seme's evil parents, the Seme and Uke will help unlock an even bigger door on our earth that will allow any evil alternate being to cross over into our world freely with our restrictions. That's why the Uke and Seme haven't been transported to the evil alternate earth yet, they are working with the evil beings! It's going to be crazy because in the end the biggere door they open will merge the evil earth and our world together! It's going to be carnage! Everyone has an evil twin all of sudden lol!
Earth is only considered 'pure' when placed next to the alternate evil earth! The Seme was authored to show that, innocent of people can be corrupted by circumstances. Although he wasn't born evil he did turn so because of the evil parents who hijacked his family. People have grey lines, they embody both good and evil where as evil earth dwellers 'only' embody evil! The Seme's good side will shine through though when the Evil Alternate Uke kidnaps the Uke and pretends to him. The Uke, is held on the evil earth and meets Seme's real parents who are still alive! The Seme is going to go all hero and good lol.
A while, it's a whole arc! You see, their evil dobblegangers get worried that the Seme might be influenced in a good way by the Uke and might drop the promise of helping out with opening the door. This is why they kidnap the Uke and replace him with the evil dobbleganger. The evil dobbleganger Uke starts manipulating the Seme to continue with opening the door and he falls for it. Meanwhile the real Uke is taken to evil earth where he finds the Seme's real parents trapped there! He really wants to save the Seme, as a kid he was too weak to save him but now he knows he has the strength to do so! He kills the evil Seme dobbleganger and manage to escape back to their pure earth and find that the Seme has opened the door. The whole world is in chaos, they were too late. However, the Seme's real parents sacrifice themselves to destroy the door and mirror and tell the Seme they've always loved him and were happy to see him all grown up. They tell him they're glad he has a reliable partner, the Uke, and they hope he lives his life happily from now on. They thank the Uke for loving their son. The parents then sacrifice themselves, destroying the evil earth, mirror and door! We then get a time skip of 4years, the Seme and Uke are together and have now opened an orphanage at the Seme's house. They house orphaned kids whose parents died because of the evil earth. The Seme is still an author but he writes more happy stories now, the Uke is a full time "Dad and teacher" to the orphans. He dropped out of police school and decided helping kids was better suited to him. That's how it ends. :)
The ones you saw die when they were kids are the parent's evil dobblegangers. Remember, I said the parents were taken to the evil earth and their evil dobblegangers took over the lives on earth and abused young Seme who then made a deal to have the evil dobblegangers killed in order to help his own evil dobbleganger and the Uke's dobbleganger to open the door. Although, the Seme doesn't know the parents killed were not his real parents but imposters. He thinks it's real parents he had killed.
I’m so confused at this point. Someone please give me all the spoilers, detailed as you can. What is the person in the mirror and how it connects with the adopted son Seme? Why is the seme going after MC? What does MC have to do with the mirror and seme? Etc. Anyone can give me spoilers on top of spoilers.
Would appreciate it to enlighten my dumb brain. Thanks. (⌒▽⌒)