Regarding Darkin Lore.

The Darkin's have always been my favorite "race" in Runeterra ever since Aatrox was released, which I believe marked the reveal of the Darkin. I'm just fascinated with the whole dark and mysterious theme that they bring to the table. I've got a few questions though, regarding Kayn's release. Rhaast appears to be a Darkin (through his audio files and what not) which sparks an interest in me, for he's not in any way a humanoid being, or just a creature you might say. So does this mean that Aatrox isn't the actual name of the character, but the blade itself? It would make sense, for Aatrox's title is "The Darkin Blade". This would also tie in how Kayn has the option to become corrupt by Rhaast in one form, whereas there is no interaction between Rhaast and Kayn in his Assassin form. It also came to my attention, that Rhaast has special interections with Varus, when he taunts, pointing out that that the "5 of us will lay waste to this realm". This doesn't make sense to me though, because Varus's name was Varus before the corruption. So either his lore is just outdated, or i'm missing something here. Also, does this make Varus the goop that took over his lower half, is it the bow, or is it both?