Matter the Cost. Leo Demonhart has finally unveiled his true identity as the Hero to the Demon Queen Echidna, and his confession comes with a shocking revelation-he is the guardian of a Philosopher's Stone. If Echidna wishes to obtain the stone and bring peace to her homeland, she'll have to get past Leo first. In a decisive battle against the man who has quit his mission of protecting humanity, Echidna and the Four Great Guardians face a momentous choice: Must they put an end to the Hero once and for all?