Obami is surprisingly fine with Miku "digging" into his secrets because he himself doesn't fully understand his own origin. Subverting the Hero/Villain Archetype
The 800-year seal provided these exact conditions. The knowledge and memories of the original Idaten who sacrificed themselves to create the seal were "disassembled and reassembled" by the dying demons' pleas, creating a hybrid entity.
The most significant reveal in this episode is the theory regarding the Demon Lord Obami's identity. Ysley deduces that Obami is likely an .