Okay, that's just straight up stupid writing. Him having an amnesia is whatever, that's just another trope that could be used outstandingly by great authors. But NOT reporting it when there's a gravely injured teacher alongside him? We don't even need to go meta here, that's very irresponsible...
A (self-proclaimed) Evil God who pretend to be a human named "Wakaba Hiiro" to have fun better understand human. Additionally, way back when we first met her and Guli-Guli, we learn that she's higher in the totem pole than him despite both being Gods.
The artwork on this series is fantastic! I just love how the artist depicted the Lord of Heaven as that winged beast. And because I'm an FGO player, I immediately get why they depict the "hub dimension" to Heaven as Gogh's "Starry Night."