A title that crossed my radar as being associated with a whiff of shoujo-ai; though when I'd picked up the first volume of manga, I just found it incoherent and incomprehensible, not knowing who these people were (or being easily able to distinguish the b&w line drawing girls). The anime was slightly more coherent, though the ragged fade between the two parallel storylines was not well handled, failing to introduce the characters in Japan, or even make clear that this was a bit later and the look-alike of Rui and Ryohei were the characters from the South American thread. The viewer wasn't told as much as any of the characters would have known about what was going on, even.
In the end, the plot was just about explained and resolved, but with a mass of unexplained loose ends (who were those beast-headed people in the early episodes, and why didn't they have anything to do with the ending? Where did the jinki-tech (and Ancient Jinkis) come from?
It was redeemed by very catchy J-pop endpieces, though.
[Later] the incomprehensibility of the manga is apparently explained by Jinki:Extend being a follow-up/complement to an earlier title, Jinki, which followed the South America thread.