An fgo headcanon that is dear to my heart is that post-canon, Chaldea, as in the actual building, grows sentient- because when you stuff so much magic and blood and love in a single facility it’s bound to have consequences. Sometimes employees run into a person who is sometimes black-haired and sometimes red-haired and always helpful and always silent. A person who knows the ins and outs of the facility, who can help you when you’re lost, who can find any misplaced item, who can point precisely where the system failure is, but features on no list whatsoever.
(Director Goredolf is the only one who knows whose face exactly the facility is borrowing. Directeur Goredolf is the only one who knows who that building is grieving.)
Anyway Guda as a servant is summonable in many different classes but if you get a Caster who goes by Chaldea’s Master do not be fooled that’s not Guda that’s the actual building committing blatant identity theft.
Generally speaking tho I love the idea oc Chaldea as a character even outside of the whole servant business. Literally cannot fucking stop thinking about Chaldea grieving the one human who filled it with so much blood and so many ghosts that it had no choice but to grow a soul. I think a story exploring anyone’s opinion on Guda post-canon would be super interesting and I’d love to write it someday, but what Chaldea has that the likes of Goredolf or Meuniere do not is that as a building it gets to be incredibly not fucking normal about its favorite human. I’m sure the staff will all have diversified opinions but ultimately they’re all regular humans and that means if I want to write truly unhinged stuff I’m gonna have to go for the building. House that stole your face so the world would not forget you.
The building is wrong about Guda. Obviously. You can count on one hand the amount of people who truly knew Guda, because Guda is a fucking mess of playing pretend and hiding shit from others. But Chaldea, being a building that witnessed a lot more of Guda’s life than the average joe who only saw them like eight hours a day, is wrong in a drastically different way than Goredolf is wrong or Meuniere is wrong. If you want to know the truth of what happened in Chaldea and who its master was you NEED the building’s testimony to complete the human ones.
Chaldea, as a building, has no concept of “death.” It understands destruction and rebirth. As far as it is concerned, Guda is not “dead,” they’re “gone.” So it’s their duty to wait for their dear friend. To keep a place where they can come back and be safe when they get rebuilt. To keep a good reputation for them by interacting with the new staff by wearing their face. Yes, this, too, is grieving, even if not a grieving as humans grieve.
Chaldea doesn’t move like a person but they don’t move like an animal either. In fact talking to it is incredibly disorienting because even if they project the image of a human body… It’s just that. A projection. Their real body is all around you. You may be speaking to it one moment, qnd the next it’ll look like it teleported behind you, and the next the body is gone and instead five reflections of the same face are talking to you through a mirror. And from Chaldea’s perspective they haven’t moved at all it’s like moving a sockpuppet. Get bamboozled idiot.
Alternatively: Concept. Post-canon. The chaldea organisation has been dismantled. Years later, various mages head to the pole to investigate the facility and discover finally what TRULY happened during the bleaching of the earth. Misfortune keeps befalling the expedition however. Members fall sick. A bunch of shit in the facility is unstable so they keep getting shelves or snow falling on their faces. Sometimes they get lost for hours walking in circles. One of them get serious injuries from an open control panel filled with sparks. Doors close on people who try to cross them. It keeps escalating and becoming more and more violent until it becomes fairly obvious that the building itself is telling them to fuck off. Because why wouldn’t it? You people abandoned it. Didn’t it fight alongside all of you to save humanity? Didn’t it keep all of you safe inside its belly while time ravaged the outside? AND YOU ABANDONED IT! Fuck you fuck you FUCK YOU. And you’re mages too, it knows what mages are like, dangerous selfish annoying the last time a new mage stepped in this facility an army of oprichniki followed tearing it apart tearing its people apart FUCK OFF FUCK OFF FUCK OFF YOU ABANDONED THIS FACILITY YOU ARE A DANGER TO IT YOU ARE A DANGER TO ITS MASTER WHENEVER THEY WILL GET REBUILT FUCK YOU FUCK YOU FUCK YOU LEAVE.