Board Thread:Questions and Answers/@comment-108.28.238.161-20131101034440/@comment-16571503-20131102064100

Nemesis Horizon, the place where Amaterasu was hidden and they open it using the monolith, a lot of souls and Nu faking as the Successor by the synchronization.

I would guess that Nu was the Yata no Kagami (the mirror to fooled Amaterasu that there was someone more beautiful then her, but was he mirror image)