I've finished watching all 10 episodes and I think I have more questions than answers...
Not sure if this series came to fruition after the success of "Kinn-Porsche" but it seems that BLs with plots or at least some side stories that include gangs, illegal activities or guns are increasing a bit.

This series had the original premise of a forest ranger (Din) who found out all the bad deeds done by Chief Ingpha and wanted to expose him. On the road to that, he falls in love with Ken and both have to suffer a premature death at the hands of Ingpha and fall off a cliff in the process (similar to what Max and Tul go through in "Manner of Death"). The only original points I give to this series is how they handled Din's fake death. His sister Sai and Sai's husband, Dr. Chayeol, take him to South Korea to get treatment and stumble upon the chance of an identity switch when a Taiwanese patient (Peter Lue) dies in the hospital. To avoid any trouble with the Taiwanese authorities, Din takes Peter Lue's identity by getting his face while he is reported as dead so Ingpha stops looking for him. Up to this point, the series sounded quite interesting using a plot similar to John Travolta and Nicholas Cage's movie "Face/Off" were both undergo face transplants (except both are alive in the movie unlike this series)... however, afterwards, this series got many things wrong.

I read comments about this being a mystery/thriller type BL so, it should be somewhat confusing to keep the mystery going... I agree to some extent because, yes, I don't want any mystery series to be predictable enough for me to lose interest by episode 5 if I already know who did it. However, this series left me with many questions after each episode that I'm not sure any series, even a mystery one, should leave... for example (I might switch between Peter Lue and Din's names but you know he is the same character by now):
1. Why is Peter Lue wearing turtlenecks and leather gloves almost all the time? The necklace that Din got from the monk and that Ken finds during one of their fights seems like the only reason to wear a turtleneck... but the gloves? He is not hiding a scar or a specific tattoo that Ken could recognize, so it makes no sense.
2. If Ken goes to China why can't Din just contact him at some point during all this? Instead, Ken spends countless times crying and remembering his boyfriend. Then, Ken has to fight this mysterious man in black (who is Peter Lue) because apparently he is trying to prevent Ken from getting involved and keep him safe... noble action but without telling him or anyone else of his intentions, Peter Lue just confuses Ken and the viewers when we have to spend several episodes figuring if he is good or bad.
3. Why Sai is the only family member aware of Peter Lue's identity? Her parents and her brother Hin have no clue until Hin discovers everything in episode 8-9 and the mother suspects it around episode 9-10, but never really finds out. I also don't get how Dr. Chayeol is qualified to perform such a complicated-looking surgery, but I guess he is a genius doctor.
4. Din finds out the illegal activities by Chief Ingpha and also discovers that his boss is involved by getting payments from Ingpha... what happened to Din's superior in all this?
5. How is Inspector Don involved in all this? He seems to be part of Ingpha's group but later we know he is actually helping Peter Lue/Din find evidence against Ingpha but I never found a reason for him to be helping Din other than he is a righteous police officer like Din was a righteous forest ranger. Same with the second doctor who works for Ingpha to perform the organ trafficking but is also helping the police.
6. Ingpha even has an organ trafficking network in episode 10 that comes out of nowhere as I thought the drugs and the illegal wood were his only businesses.
7. The ending... OMG... after all the things both characters go through only to have Peter Lue charged with murder and him having to vanish again?! Now, I do think he is hiding somewhere but Ken and him will reunite at Sai's wedding that will be on the 7th day of the 7th month, the date that linked Ken and Din in the series. But still, the open ended finale was a bit disappointing after 10 episodes of figuring things out in the series.

Now, kudos to Haii (playing Ken) as he has to adapt and develop chemistry with two different actors who portrayed Din (played by Kut before "dying" and by Boom when he becomes Peter Lue). I think Haii navigated through many emotions in this series, from falling in love to almost dying due to Din's findings, to thinking he lost Din, to struggling when he begins to develop feelings for Peter Lue while still clinging to the thought of Din, to feeling betrayed when he finds out the truth of Din being Peter Lue, to accepting the "new" Din, etc. Haii does an adequate job of taking me through all those feelings (with some minor exaggerations that I can overlook). Kut and Boom had to act in very different situations so you can't compare their portrayal of Din. Both do have some good moments but thanks to questionable directing and editing, most of their moments end up being confusing to the viewer with flashbacks that come out of nowhere and situations that were not properly connected.
The other characters are fillers for the most part... Marc Pahun must be enjoying not being a GMMTV exclusive anymore as he is appearing on 3 BL shows at the same time (this one, as one of the leads in "Past-Senger" and in some of the "Our Skyy 2" episodes) and in here, he is able to showcase a bit more of his acting skills by playing some relevant role as Sai and Din's brother... too bad some of his moments get lost in silly or comedic situations that were highly irrelevant and his interactions with Sai when he finds out the truth could have been exploited much more but poor editing and directing switched out of the scene to have another useless Ken/Peter Lue moment. And, his relationship with Payu was never explored and aside from a brief steamy scene between them, we got nothing worth remembering. Other side characters like Ken's dad (who we saw as the head of the family in "Kinn-Porsche") is just relegated to being a restaurant owner in China; Din's dad (who we saw in "The Miracle of Teddy Bear" and other shows) barely has any lines in this series; Poppy (playing Inspector Don) seems to be present in all major scenes according to the flashbacks, but we never really know anything about how he fits in this puzzle; Ken's friends seem wasted as we barely got anything useful from them and instead, we got a healthy dose of DeeDee in the final episodes with him being one of the most irrelevant and dumb characters in this series. And, Ingpha's main bad guy is annoying with the horrendous laugh all the time... I know they want to picture him as a psychopath or a sociopath or both, but the laughter is just poorly done and quite distracting.

As for the sillier moments, all have to focus on the chaos that episode 10 was. First, all the killings done by Din/Peter Lue are just a joke... he faces 5 gunmen who cannot hit him once with semiautomatic guns and pistols... then he does his best impersonation of James Bond and shoots some of them, throws knives at others, and slits 2-3 throats with his knife without a drop of blood staining his face or clothes... when you slit someone's throat, the amount of blood that gushes out is quite significant... he also shoots a bad guy in the head at point-blank range and he is pristine and clean during all that, quite unbelievable. Then, he faces Ingpha who is holding Sai hostage... Ingpha still has no clue who he is until he shows him the camera/mic he dropped when they met in the forest for the first time and that led to him being shot at later. In the blink of an eye, Ingpha recognizes Din who suddenly thinks this is a Western movie and pulls out his gun and shoots the chief in the shoulder so precisely and without affecting Sai (who was sitting on Ingpha's lap and suddenly disappears from the screen until many frames later when we see her sitting unharmed on top of a rock). Then, in a weird twist, Din/Peter Lue is so revenge-thirsty that instead of bringing the chief to justice, he just kills him execution-style with a shot right in the middle of the forehead. The cold-blooded execution makes no sense... I mean, I understand Din is harboring too much hate towards the man who ruined his life, forced him to take a dead's man identity and separated him from his family, friends and boyfriend... but to kill Ingpha like that seems a bit anti-climactic for the man who wanted to expose Ingpha's actions.

In the end, the show was not the worst BL I've seen but it left the lingering feeling of "what might have been" if directing, editing, writing and acting would have come together, maybe this would have been a masterpiece given the plot... instead, it became just one more BL that failed to meet my expectations.