God I fucking love. Castoria. You meet her and she looks exactly like all the other king arthurs in the game. If you know literally anything about Fate as a serie you know that's the face of the Protagonist (tm). The two of you are stuck in the forest of fucked up amnesia, meaning you've got to work together to get out. She's a good girl!! It's obvious! Look at her design! Look at her big smile! She's obviously a genki girl!!
Later you learn she's the hero propheticed to save the land. She's a heroic figure! She's on the good side of the alignment chart for sure!! She's even got cute anxiety moments, isn't she adorable and harmless!!
But if you pay attention you start noticing odd things. She doesn't do real magic, it's all petty tricks for crimes, breaking and entering and lockpicking. In any given situation she seems to be analysing possible escape routes, the entirerity of chapter 1 is her trying to figure out who you are, how you can all leave, and constantly reminding you lay low, don't make wave, don't make them angry.. And she never talk about her past- the little you learn all comes from OTHER characters telling you about her.
And then. You learn the truth. Your genki girl Castoria isn't a genki girl at all. She's an extremely bitter and cynical girl whose entire monologue the entire time is basically "I hope everyone here goes to hell no matter what." The only reason why she remembered Barghest's name for so long is because she is genuinely that petty. She tried to kill herself hours prior of the first chapter. She hates this world she's been tasked to save and doesn't give a single shit about seeing it end.
And the kicker: That event that lead to the two of you meeting ? The amnesia thing?
She wasn't amnesiac at all. She lied to you. She deliberately took advantage of your memory loss because she's desperately lonely and she thought that was her one shot, if only for a moment, to have something close to a real friend.
Everyone is a liar in this chapter. Some literally cannot help it (Oberon, Habetrot) some lie to cope (Morgan, Guda) but Castoria is the only one I would truly consider a compulsive liar. Her every dialogue choice is based on the very simple question of "how likely are they to lash out and hurt me if I say what I truly mean." She lies, and she lies on purpose, to everyone. And she is extremely good at it because she is in fact totally genuine in a lot of her actions (she does mean it when she's cringing or embarrassed) so of course you assume someone who would be honest about such obvious "weaknesses" wouldn't be able to lie at all. But that's the point. If you look cute and harmless people will take advantage of you but they will not kill you. She literally needed to get slapped with A-rank Madness Enhancement to be just 10% more honest about how she feels. Castoria has among the highest bond point requirements of all servants, and her Summer version is even worse because she's THAT much of a brick wall to talk to.
You can't make Castoria worse. She's already at the rock bottom of cynicism. If you stuck her in the whump torture basement she'd react exactly as she does now because her entire life is already the whump torture basement. And at the same time you can't fix her either. There's nothing to fix. There's nothing wrong with her. That's the tragedy of it. She's a normal person who was forced to go through unspeakable suffering. She's normal!! The world is what's broken!! She doesn't wear her trauma like brambles on her skin you can just pick out, she grew around it like a mishapen tree. It affected the core of her behavior she would literally be a different person otherwise. Castoria won't break down if you stick her in the torture basement but also she'll never be truly at ease in the outside world either. Even in the most peaceful stardew valley scenario she will interact with everyone with the mindset of a paranoid rat who lies compulsively because she doesn't know any other way to be. The fucking summer event is 90% dumb fun and she's still lying through her teeth the entire time because she likes a grand total of two people and she still doesn't trust either of them. You can get this girl out of Fairy Britain but you can't scrub Fairy Britain off this girl.
Anyways. Love this girl who is an animal. Beast and Guda’s pet and a fairy of the demon boar clan and Taiga’s kin and a bunny who wants to hunt people for sports. Feral little thing slowly undoing her own domestication. Wretched beast of a girl.