My favorite character arc/story arc is Citan's because while you have to read between the lines and have a little bit of context outside the game itself (which is a huge problem with it for a lot of Westerners who've never watched or read another piece of Japanese media in their lives or at least one with samurai/their concepts involved and/or who go in with an American Christian mindset and miss it all, which is where they often get thrown and are like WTF BIGGEST ASSHOLE EVER) it's one of the deepest of the game in a sense, touching on everything from interpretation of religion to the meaning of loyalty and duty (and changing said allegiances), and more.
If you go into it with an understanding of Japanese culture - ESPECIALLY samurai tropes which he's very much based upon - and a view of him *as* bound to obedience/oath/duty per samurai tropes - and an understanding of the concept of Satan as a once loyal yet pragmatic and aware servant of God that can no longer withstand the contradictions of "God is good/good God just committed genocide, so is God actually Bad God or is genocide good" and can't decide whether to side with God or humanity before choosing humanity (basically the antithesis of the American Christian teaching) -
*that* view really makes Citan's arc one of the most poignant of the game, as you realize,
when he finally does take back his sword and turn it against Solaris to save everyone and eventually against Deus/YHVH himself... yet having had to both do horrible things and suffer a Pyrrhic victory in the end as a result... that you were, all the while, watching that aforementioned progression from servant of God convinced God is absolute good to enemy of God on realizing absolute power corrupts absolutely, from loyal samurai to free ronin... and that his choice to free himself and help free humanity from servitude to Solaris parallel's Fei's to save humanity and free the Wave Existence from servitude to humanity.
tl:dr Citan isn't just about making Fei do all the work and forcing people into cannibalism for the sake of being a traitorous dick, and if that's anyone's serious non-shitposting view of his arc, I *highly* recommend
at the very least reading Paradise Lost and a few history books on samurai
EDIT TO ADD: Also, one other thing I like about Citan is, again because this is actually handled better than the named disorder in the game but the signs are definitely there if you look - he and Midori both seem to be on the autism spectrum, and
neither are lesser for it. (In fact, Citan's portrayal really holds up even now as a portrayal of an adult autistic man not as Rain Man/inspirational yet pathetic, but as valid in setting) I could only wish Fei's condition had been written *half* as well and half as sensitively, but I think part of that is that there's enough people on the spectrum in gaming that it just naturally appeared for whomever was writing him, whereas the amount of
out plural people in Japan or in the games industry at all is pretty few even today, and was likely 0 in 90s Japan.
And one final edit: One reason I like going with my endgame party as Citan and Billy or Citan and Chuchu backing up Fei is for me it actually completes the allegory to finish the story that way: with Billy, it's all three of the people that Deus's existence and dominance have directly affected the most finally settling matters, and with Chuchu it's like an anticolonialist concept -
the survivor/goddess of a genocided indigenous culture that Solaris and Deus (and everyone else to be honest) sees as a joke gets to fight and win against the being that tried to stomp her and her people out for good.