I don't think Chaos is sentient to that degree. I imagine it's more that humankind is very orderly in its mannerisms and social constructs; and what opposes chaos better than order?
Yeah well, I agree with you in part.
Chaos, as I understood by the numerous explanations mostly given in the novel, appears to have some kind of intention. Not exactly sentient, but not exactly a "force of nature" or merely "opposite of order".
Chaos is explained to be born from humans in the novel. In Aria we see that it has an affinity for Soma, and it defends itself against Soma's attack. That's intention. Sure, one could argue that it is defending itself like an anemone does - no intention at all, it simply
does. However, we know that Chaos takes Soma's souls away, targets him multiple times, and is defending itself specifically so Soma heeds the call for a Dark Lord. It is more like an animal than a plant. An animal can't exactly "reason", but it understands such things as not attacking animals bigger than itself, or to evaluate the costs of pursuing certain goals while being in a vulnerable state.
Death explains, also, that "human death" is merely one part of what comprises Chaos -- implying it has more "parts" comprising it. And it is confirmed that monsters are born out of chaos, too. As we know, monsters are pretty freaking misanthropic, with VERY few exceptions. Death, who is born from Chaos, has a pretty cunning mind and pretty clear objectives. How, if he was born and is made from the thing that has no intention at all? Death is not "affected by chaos", Death comes from it. Is made of it. And the same is true for many other demons with clear objectives.
To me, Chaos appears to be some sort of "collective consciouness" comprising everything negative about mankind, such as fear or death - maybe even including a desire for self destruction. Again, not exactly "sentient" as we understand it, but also not exactly a "force of nature" as things like "gravity" or "storms".
Keywords here:
Not exactly. I'm not saying Chaos is NOT one or the other, I'm saying I don't think Chaos is entirely one thing or the other.
EDIT: One important thing I forgot to add: Saying Chaos is "the opposite of order" implies that it has been always here as part of the universe ever since it began - as a counter to order. This conclusion is not correct for the Castlevania context, as it is clearly stated Chaos is born from mankind. Chaos exists because humans do. As a product of humans, Chaos is not "as old as the universe". It may be the opposite of order, but not as in "order of all things", but more like "order imposed by humans".