Theme naming: Hyde/EXS explanation
While Hyde’s name doesn’t really have any specific theme to it, his name does have some correlation to what exactly In-Births and Voids are, though it’s most likely coincidence. In Hilda’s Chronicle Mode story (Road To The Under Night...), Kuon brings up The Strange Case of Dr. Jekyll And Mr Hyde and how it ties in with EXS and In-Births. To put it rather simple terms, everyone on Earth has the powers of EXS dormant within them, and only the bite of a Void can awaken that EXS. Think of it as a balloon; to release the air, you need to open up a certain area to let it escape, that area of escape for us would be the bite wound left by a Void, which releases the EXS.
Going back to the comparison, a balloon needs to have a certain amount of air inside to keep it stable, removing too much would cause it to deflate. Let’s say whatever air that is removed is replaced by Helium and gives the balloon the ability to “fly”; much like that, the EXS within us is replaced with something else entirely, which is what gives us our In-Birth abilities.
This unknown element also, in a sense, affects our minds and creates another personality, or “self”, that lays dormant within us, similar to the formula that Jekyll created which in turn, spawned Edward Hyde. The more EXS we take in, the more this other “self” becomes prominent and starts taking over more and more, as to what happened to Jekyll when he consumed too much of the formula. Soon, that other “self” will take over and from there, our real self would essentially die and the transformation into a Void will begin.