If you liked the Saiyuki anime, the Anime-Planet community thinks you'd like:
It is the early 1920s, and New York City has a problem of evil proportions – demons. With devil worshipping on the rise, foul spirits and monsters have begun to surface, causing fear and panic in their wake. Combating this threat is the Magdalene Order – a group of religious officials charged with exorcising the evil that is spreading throughout the city. Rosette Christopher is a young nun who takes on missions alongside her contracted partner – a young demon named Chrono. Now it is up to this unlikely pair to wield God’s power – and plenty of holy bullets – to destroy the menace in front of them and confront the demons of their past.
If you liked Saiyuki,you would like Chrono too because they are both based on lessons of life like religious beliefs, believing in yourself, or making the right decisions at critical times. They have both well-made animation and gorgeous characters. If you want to watch another heartwarming, deep, funny and full of action series, then you're looking for Chrono.
Tsuzuki Asato is a shinigami: a guardian of death. Acting as an investigator in Juuouchou, the bureau in charge of ensuring that each soul passes through the cycle of life naturally, his job often involves dealing with those who would disrupt this cycle. His life after death is about to change, however, as he is assigned a new partner, Kurosaki Hisoka, for a case in Nagasaki - a case seeming to involve some sort of vampire. But the two shinigami soon find that something deeper lies behind this blood-sucking menace...
Descendants of Darkness and Saiyuki both have decent detective stories. Both are fairly predictable, but decent.
For those who enjoy boy-love Saiyuki I think has the better relationship, because the characters are less, well Descendants of Darkness gives the main characters a somewhat flat personality, and it can be a bit of a drawback at times. However, on the same token Descendants of Darkness also has a much more satisfying amount of fan-service (if, as seems to always happen, it does detract from the story a bit, which is a shame).
Saiyuki -is- significantly longer at 50 eps vs. only 13 though, which could be an issue for you if you don't like or you prefer longer or shorter stories as the case may be.
Ultimately though, these two anime are roughly on par with one-another for quality and very similar in content without being too similar.
Another thing to consider is that while Descendants of Darkness is an absolutely beautiful gothic and macabre world, Saiyuki is very much of a kind of. .. illustrious beauty. Alabaster pillars, colorful outfits and so forth permeate the majority of the show. Though by pure quantity and not percentage all of its short moments of the macabre may add up to just as much as is had by Descendants of Darkness heh heh.
A mysterious monkey-tailed boy named Goku teams up with a teenage computer-wiz girl named Bulma to search for the mystic Dragon Balls. According to legend, whoever collects all 7 Dragon Balls will have any one wish granted. Join Goku in this hilarious anime masterpiece, as he races and battles to save the world from the forces of darkness. Who will find the balls first?
While reading "The Universe of the Four Gods", best friends Miaka and Yui are mysteriously transported into a strange world full of magic and unfamiliar faces. As if their arrival was determined by fate, Miaka is revered as the Priestess of Suzaku, the savior of their warring country, who was destined to arrived in a flash of light, from a land far away. Betrayal, love, and heartache accompany this fantasy-filled tale of friendships torn apart, and hope that never fades.
With a history of leading a motorcycle gang and getting bad grades in school, why would 22 year old Onizuka ever want to become a teacher? Is it to educate young minds or spread the joy of education? Sure, if it involves being able to look up high school girls' skirts! Watch as this would-be educator uses his own life lessons and unconstituted methods as a means to control a delinquent class of students -- students who certainly aren't as happy to have him as a teacher as he is happy to be teaching...