I would say it's one of the animes that has a high amount of reference or
inference to Christianity and Christian symbolism throughout.For example
Kyosuke's foster mom is a nominal Christian also there are a lot of crosses that keep on appearing throughtou the series.One episode takes place in
a mission school for girls,at one point Kyosuke compares himself to Christ.
Mostly it's a fun adventure/sci fi series.My favorite character is Maya the
Flicker that rescues Kysouke after he's "killed".Ok so it helps that Maya is
played by Kelly Sheridan in the dub.Another favorite is Komugi the slightly
wacky Mutant Rabbit Nurse(she's not really a rabbit she just dresses in
a rabbit custome).Komugi was so popular that she got spun-off into her
own OVA:Nurse Witch Komugi a parody of the Magic Girl genre.
The ending is surprising and rather poignant.
All in all a most see if you want to watch a good anime that stretches
your imagination.