Spoiler Alert
Revelation from Volume 10 of the manga that basically spans throughout most versions: So basically when the series starts you kind of think it's just a regular we find each other through each reincarnation kind of dealie, but then you eventually find out Charlie/Byunghee is immortal! Due to a curse from like, Heian Era Japan by a band of roving witch fox spirit fujos who did so because of his history of as a philanderer, forcing him to try to get this one person (Julian) to truly love him in order for his soul to be at rest. Throughout the years and Julian's lifetimes, Charlie has come close but also Julian has a tendency to die very tragic deaths before the curse can be lifted. Julian, who kind of has a lot of baggage around being controlled by expectations of other ppl, particularly his overbearing family, is quite understandably upset, when he finds this out. It really dampens his love boner, and the series after this is found out is centered about what it means to have agency, as well as Julian's misgivings about whether Charlie actually loves him or forces himself to and does not know it, in order, to you know, finally die.
Ah and one other thing: as Julian's feelings grow and he regains his memories of his past lives, it is true that Charlie becomes less mortal, prone to injury, etc but also Julian becomes more immortal (it's a curse! Fujos love suffering!). So there's that.
Summaries for the Saturn Tsai Movie Triology
The HK Film Version: Three movies (2010, 2013, 2016) the first movie in the series is actually the Hong Kong arc, which, due to when the movies were made is set in the 1980s, with no mention of detectives (however, the reincarnation aspects are alluded to, near the end) and the characters are in rival syndicates, but without knowledge of the series, one would think it was just a tragic romance. HOWEVER there is one sort of wild puzzling ending to the movie, where they're on a yacht battling some triad dudes, and Charlie gets shot, and unable to save him, Julian drowns. In a nod to Charlie's immortality in the manga/anime, in post-credits scene, Charlie after being shot, sort of just gets up, wounds regenerated and sighs, cursed to live again for the time being.
The second movie follows Charlie, now known as Byung-hee, as a mysterious man with tons of baggage, who is assigned Julian, as his detective partner. This one is set in Los Angeles in the late 1990s/Early 2000s, and known for its playful alt-rock playlist and for a heavily memed usage of T.A.T.u's "all the things she said," during a pivotal and emotional scene. It's actually in strong contrast to the first film, it's a) a buddy cop comedy turned romance turned into car crash-esque break up end and b) very pastel and in the daylight, in a nod to the McG music videos of like 1997
The third movie is set in the present day, as a road trip movie with the characters in their current incarnations, as wanderers of the world, collecting objects (like the manga series) that give details to their complicated and long history. Told as multiple stories within a story, long sequences of desert driving, and also multiple flashbacks to their previous selves— there's some like scenes that involve the truth of the curse in Heian Era Japan, some Renaissance Europe naughty art monks in love shit,oh yeah obviously the one where they are in symbolist/impressionist era France and one Julian is a painter and Chartlie is a composer, uhhh prob one where Julian is reincarnated as a goldfish, mood is lighter than the first movie, darker than the beginning of the second, shoegazy soundtrack, different styles. Asks the question, would you still love me if I was, ok not a worm, but a goldfish who forgets you every 25 seconds.