Upgrading to Angel of Death

[icewolf34]

Are there any other requirements to upgrade an Angel to the Angel of Death besides having Guilds and having level 4+? I finished researching Guilds last turn, and I have an Angel of level 5, but I can't upgrade it. It's outside my borders, if that matters... does it need to be in a city with a specific building or something?

 

[Derf]

IIRC, you need to be within your own borders to upgrade, and if a specific building is required, in a city with that building.
I think the Kuriotates are the only ones who don't need to be in their own borders to upgrade, but that might just be in RifE

 

[Emptiness]

In base FfH2 you need to be in your borders and within the city work zone of a city that has the required building (if any), unless the unit is one of the Doviello melee line units, which use a special mechanic to allow them to upgrade anywhere.