Evil City, stuck. Need some advice.

[Zero, Dark Knight]

the boss of the swamp is greyed out at "Unlock" Been stuck at trying to unlock it for like 4-5 days and can't work it out.

Is it Dr. Mad and his "nectar" line of quests? or is it virtue/malice dialogues? is it something to do with the Holy City? or do I need to farm the rare monster, Sacred Bird Chick?
or is it something else entirely ?

I don't even mind the spoilers of you outright telling me what dialogue stuff it is. Thanks in advance!

[Synthar]

Obtain 10 virtue ("Patrol" loop action doesn't require resources) -> Caring Woman -> Enter Clinic -> Dr. Mad until you unlock Nectar -> Use Nectar on Man (30k destiny to make it) -> Talk with Recovered Man 8/8 -> Injured man -> Talk with Recovered man 13/13 -> Corrupted Great Bird's Return

from the discord on how to unlock the boss dungeon

[Zero, Dark Knight]

Thank you. and I don't use Discord for the record, but I still appreciate the help!