1) Give 6 nectars to Nyx and Chaos (in Chaos Gate)
2) Keep talking to Nyx and Chaos, until the former tells you to mend the Eldest Sigil in the admin chamber (ensure you have access to it first).
3) Fix it by paying the House Contractor 3142 darkness.
4) Talk to Nyx until she leaves n’ meet Chaos.
5) Find her behind a Chaos Gate and talk to her to complete the prophecy.
6) Clear it in your bedroom for the trophy n’ reward.
https://store.playstation.com/#!/tid=CUSA00572_00
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