So I wanted to do a short essay about how I think Cielo really parallels Bat some ways. LET'S SEE IF IT STAYS SHORT.
Let's start with the simplest and most obvious! Cielo and Bat are almost directly opposite each other in terms of loyalty. Cielo would quite simply die before betraying his comrades. Hell, he'd die before betraying friends, or people he doesn't know well but strike him as good people. (They just don't reach the die before failing slot that his comrades have. Bat, as you may have noticed, doesn't share Cielo's loyalty! He's a systematic backstabber who would backstab anyone as long as it would get him a better leader. He doomed his tribe and his leader with his treachery, and he continued to backstab until he came across a leader who could dominate him hard enough to keep him loyal.
But the interesting thing to me is how otherwise similar they are.
Age: Both appear to be among the younger-appearing Junkyard denizens. Cielo I'd peg as somewhere between 14-18, while Bat appears to me to be somewhere between 16-20. Most of the demons I'd actually guess to be in their early to mid twenties. Their maturity is similarly...complicated, but I'd peg them both as generally coming across as younger and relatively immature. Bat's the rebellious teen delinquent type, while Cielo's the happy go lucky quietly bitter type, but they're pretty much the only two major characters who I'd genuinely guess to be in their teens. (Well. Heat comes pretty close at times, too.)
Demon form: Obviously, they're the only two major aerial demons! Granted, they're entirely different types of demons, with Cielo being much more aerodynamic and streamlined, while Bat's demon form is much more organic appearing and, well, batlike. But the fact that they're the ONLY two named flying demons says a lot. While their elemental alignments aren't obviously parallel, with Bat being strong in wind and Cielo being strong in lightning, I'd point out that Bat does gain a weakness to Cielo's element in later fights, and while Cielo isn't actually weak to Bat's special ailment (THANK FUCK or you'd HAVE to have someone weak to him in your party when fighting him), his generic weakness is still ailments. And everyone remembers being turned into tiny helpless bats with Bat's crotchlaser.
Followers: Both of them are most comfortable following a leader that they trust. Both of them are capable of leading when it's necessary. Cielo was left in charge of the Embryon in Serph's and Gale's absence, and probably would have been okay at it if they hadn't been attacked by a tribe ten times their size. Bat presumably did similar things when the Maribel split up and Jinana was busy elsewhere. Both of them could technically handle complete independence due to falling through a wormhole and landing someplace away from anything they've ever known, though Cielo'd probably do a suicide run for a good cause eventually if he didn't find comrades and a way to eat that worked and Bat'd find a new leader fast. But they're both happiest as followers.
Gender: They're both kinda androgynous. I've had people in camp mistake Cielo for a girl, and I tend to figure that gender is about the least important part of Cielo's identity to him. Bat is a raging misogynist prick who at the same time, wears makeup and has long hair and generally tends to come across as somewhat feminine in terms of appearance and roles. I'd say there's a lot more inherent tension in Bat's androgyny than Cielo's, but they both seem to have ended up in similar places.
Mouthlasers: They both have mouthlasers. Except Bat's is also a crotchlaser. This wouldn't be worthy of notice if I could think of many other demons that did.
Past life: This is probably the most important one in terms of how they became what they are. In their past life, both of them were victims. Bat headcanons that he was raped and generally maltreated in his past life, and I have to agree because that would explain a lot about Bat. I have no particular opinion on whether or not Cielo was raped or not in his past life. If I were to speculate, I'd say his chances were a lot higher than most people's because, well, it's not like they were exactly screening OUT sexual predators in the hiring process for the people in close contact with the candidates, and those kinds of experiments historically attract unsavory people. But odds aren't fact and there's no way really of telling. However, there's the undoubted fact that he was a glorified lab rat who went mad and died, and y'know, that's a pretty sucky life!
Honestly, I would put that as the key to both how they're similar, and how they're different. Cielo clings to his comrades so fiercely in part because he doesn't want to be left alone for that or a similar fate again. Bat backstabs and distrusts and demands a strong leader in part because he never wants to be that weak again. They both seek strength in others and themselves at least in part because they're afraid of being victimized again.
In camp, it's even more complicated, because they've been interacting. And Cielo loathes Bat, and Bat...idk HEY BAT DO I GET A RELATIONSHIP MEME OUT OF ME ESSAYING? yes I'm a hooker stfu. And the whole Kuhn situation basically turned Bat from a mild ongoing threat to >>>>>>>>>>( in Cielo's opinion.
It's actually interesting because in a way, Kuhn as a person has very little to do with it. Cielo liked him, and thought of him as a comrade he could trust in, but he wasn't one of Cielo's super-ultra-love comrades. He isn't remotely interested in him romantically, sexually, and at this point at least he's not sure they were ever actually friends because clearly there were ongoing misunderstandings. But Kuhn was Embryon, and Bat took him from them. Kuhn can say he's neutral all day long, but to Cielo, it will always be Kuhn choosing Bat over the Embryon because, well, that's how it worked out in practice. And that's what hurts him, that anyone could possibly choose this sleazy traitorous bastard over the Embryon. Cielo's had one of his comrades been forced to choose between a comrade and the rest of the tribe, and that hurt him more than words can say. But at least there it was a choice between Embryon. Having a comrade choosing Bat over the Embryon...isn't nearly as bad in a lot of ways! But it still made him despise Bat a lot more, because how dare he take a member of the Embryon away from them. When it comes to what Cielo feels the Embryon deserve as opposed to the rest of the world...there's a lot of potential there for Cielo not being a nice person, and Bat ran up against that pretty hard. Sadly, Bat'll still kill him 95% of the time, and he's not willing to draw the Embryon back into an ongoing war, so he's remaining pretty pacifistic. But he'd feel a lot better if he devoured Bat a couple dozen times.
There's also the fact that Bat likes to poke at Cielo a lot more than any of the other Embryon! And some of Cielo's emotional weak spots are very obvious, and Bat is very good at twisting the truth in his verbal attacks. Cielo'll attack back, and he can usually get in a few good blows. But their verbal fights tend to follow the same pattern as their physical ones, with Cielo eventually getting pwned HARD. Another parallel is that they both will go for the verbal flaying. When Cielo loses his temper at Abaddon is really the only time anyone in the Embryon verbally flays their enemy in a manner similar to Bat's standard method. Cielo's style is completely different from Bat's, but in some ways there's some interesting parallels there.
Which is really the point of this whole essay thingy.