You might be like, "Huh?! What the hell are you even thinking Dovangel?!?!" I know I know, it seems a bit far fetched (even for me), but that doesn't make it less interesting. Inspired by Shin Megami Tensei and reading the original manga and its sequel (not including NEXT), I think there are some symbolism that Alien 9 have, more specifically in a Christian perspective.
For the Drill Clan Borgs, they have that frog-like appearance with angel wings that have drills sticking out; they protect their hosts from any kind of danger (with Yuri being a great example) and at least treat their hosts with respect and wait for them to be fully prepared for the symbiotic transformation. Does it remind you of something? Well, they're like guardian angels, of course; they guard humans from some kind of danger (except for the human symbiotic transformation, they don't do that like the Drill Clan).
Another example which relates Christianity to Alien 9 are the Sunflower Clan. They have the appearance of a sunflower, using bees as the their main method of attacking. They're a foil of the Drill Clan, having no patience with their hosts to be strong enough to do the symbiotic transformation and harming those in the process if they do the symbiotic transformation with no proper preparation. They are cunning and deceitful, giving hallucinations to those wearing them (like what they did to Yuri through the strange dreams of her slowly becoming like them). They are, in a sense, like demons/the Devil; harming and tormenting the humans they're possessing and for the case of the Devil, lulling others into his lies and do sins against God.
One another factor about this idea is that the need of taking over the world by different means; the Drill Clan tend to be more patient with their hosts and let them grow to be suitable for the transformation, while the Sunflower wants to their hosts to have the transformation immediately (even if it means killing the host in the process): kind of reminds me of how religion is spread in general.
So in that sense, the Drill Clan are like Christianity with the angelic wings and guardian angel motif, while the the Sunflower Clan are like occultist religions or Satanism, with the promising things that are false and the forceful possession.
It seems I've said what needs to be told. Truth to be told, it's really interesting how Hitoshi Tomizawa lets people to have their own interpretation of the manga, basically a way to expand the world of Alien 9, it's cool of him to do that. Anyhow, hope you enjoy your day and hope the blog post made you see things differently to the world of Alien 9.