It's super interesting to see how the Sunday Gardener (Albarino), a serial killer "who could stop anytime", in comparison with the Westland Pianist (Herstal), a serial killer haunted by PTSD. Albarino had only viewed Herstal as his own "muse" while they were having a sort of FWB/killing together relationship, and Herstal was basically dragged along onto Albraino's madness. But that slowly changed over the curse of the story, with Albarino giving the gun his father used to commit su*cide to Herstal, and Herstal basically fake killing Albarino so he wouldn't get dragged into prison along with him. It's so satisfying to see their relationship grow into something into traditional romance, when that was previously one of the disagreements that caused them to "break up".

There's also the fact that they basically risked their lives to save Hardy's child, the police officer in charge of the serial killer's case, which isn't what you'd expect for the two serial killers in question. They're not just people who'd kill, they'll help out others if it doesn't get in the way, although both of their motives are questionable.

And the best part? There's no redemption arc. There's no "they gave up on killing and happily ever after. They went off together as mu*der husbands and will remain mu*der husbands, until one of them loses interest in the other one day....

Also, what I find similarly interesting is the contrast between the side characters, Olga and Mercader, both criminal profilers. While the former basically gives no f*cks about justice (she cares more about looking at serial killers' psychology instead), Mercader instead aims to eliminate all serial killers through extreme means, like forging evidence. It's on the complete opposite scale, whether it is good to use justice to the extreme or just do the opposite; it's up for the reader to decide which side of the scale they prefer.

Child s*x Trafficking

“Why can’t I connect to your house’s Bluetooth?” Herstal yelled from the study. His tense voice was the closest thing to exasperation at this sort of moment.

“Are you kidding me?” Albarino yelled back very weakly. He felt that his abdomen didn’t seem to be bleeding anymore, which was a good sign. “You use the victim’s computer and printer to print the victim’s private parts, and then you ask the victim himself why you can’t connect to Bluetooth?!”

It's a story about how an artist moulds his creation to its final form. Hestal himself admits that he loves Albarino but the forensics scientist loves Hestal the way a creator loves his greatest creation.

por ejemplo, George Robb's girlfriend, Blanca, doesn't kill to avenge his death. We all knew the BAU already suspected George so in actuality, it didn't matter to the normal person if a evidence was faked. However, George was enjoying the cat and mouse chase. He didn't care if he died as a result, so long as the game was fair. But it wasn't. Evidence was planted. He got caught without making a mistake, so Blanca avenges not his death, but for the insult he faced in being unable to play a fair game.

Every character has their own personality, like they actually exist instead of serving as another simple foil to emphasize MC and ml's power (though they are definitely strong), but the characters you would hope to be intelligent are actually intelligent! MC and ml's identities were revealed around the second half, which is still really quick. Even after the ending, where they escape to another land, they know that they're being watched by the guards/special forces of that country (which makes it even more interesting because they have to, like, phone the boss? Of that area and casually ask if they can kill someone lol).