
Ren loves Maki's brother but he was straight and married, so he decided to go to Maki since he looks like him. He's really cruel since Maki really loved him, but he sold his DNA and memories for Maki's brother's company. He died from the extraction process, and because this is illegal, the people involved in this operation were arrested. As they were investigated by the Burea Protection Team, Maki saw Ren's and other people's corpse.
Ren's dna and memories were then put into the hands of another illegal operators as they were sold, and they made the robot "Arata" using these. The robot was about to get shipped, and sold, when Maki's friend (sorry, i forgot his same) bought Arata for Maki as a "birthday present".
Arata's imprinting function on Maki was cancelled only, and not his memories and emotions. Simply, he loves Maki, and all those six months of waiting stuck with those memories and emotions, made him feel love and not the imprinting love for Maki.
Basically, Arata has Ren's dna (his body and voice) and memories, think of it like those mangas where the main character died and was transferred to another person's body and he has this another person's memories too. (Probably like the "Best Actors Life: Take Two" from Webcomics)

I really love this manga, but personally I wish it was longer to see the seme change for the better and for him to be worthy of Aoi. He's a player, a gambler, a freeloader, in his past, and he took Aoi's love for granted. He returned Aoi's love, but I just hope we we're able to see his character growth, since a part of me still don't like him. But I get that he's an actor, so of course, he'll earn money himself and not resort to gamble and freeload Aoi (for real, who'd take a lover who just empties your pocket). But the player part, hmmmm. I just hope he changes, and if there's a sequel, I'll be dying to read it. And a sequel of course for the Lt.
Tbh, I'd rather not see the seme die than what ya'll are mostly thinking. I want him to suffer everyday of his life because of all the shizzles he did to the poor uke and the boy who died. ヽ(`Д´)ノ