Sheol-gurrath needed a host - euclidean space was slowly rendering her (it?) inert, and she had no way to return to the interstellar void on her own. And then she was introduced to (read: injected into) Szar, a euclidean lifeform on the brink of death who just so happened to have space in his psyche where some non-existent nerve connections used to be.
And so a new Bladebound was born.