Okay, but how would the round table peeps react? Especially since Arthur and Jekyll/Hyde used to be enemies?
(I’m guessing you mean from the London Singularity when the Artoria Alter was created? I haven’t seen a lot of the other series, but I am slowly going through them)
All joking aside, I figure that they would all have a variety of reactions.
Mash: Would be extremely happy to see how happy they are together. And silently relieved that Hyde is not as... Destructive and stab happy
Lancelot: Honestly? Probably wouldn’t give it much thought other than “How did Mordred, the kid who stabs all her meat to eat it, get into a relationship better than mine”. Though he would be happy for her in the end
Tristan: Wax woeful songs about how he won’t ever find love again or how his love life is doomed to fail while saying something about how they’re so good together. Mordred is simultaneously warmed by how he sees their relationship while annoyed at him for the “Woe is Me” shit
Bedivere: More curious on how they got together than anything. Once he’s told, he gives Mordred wishes for a good relationship
Gawain: Kind of over protective in a way? I’ve always seen their relationship as an older brother and younger sister so he is very suspicious of Hyde’s intentions. Jekyll assures him that they both want her to be happy and safe. (Mordred does find out eventually and is kind of pissed he’d do that)
Arthur: He would be happy for them and give them his blessing while wondering how his son would meet someone like Jekyll/Hyde. Which again, pisses Mordred off.
Artoria: Much like Gawain, is a bit over protective over Mordred. With them, I’ve always thought that their relationship would start to be better once summoned to Chaldea. Unlike Gawain, she’s a lot more sneaky about her investigations. She wouldn’t want to risk damaging the relationship they built by seeming like a helicopter parent. In the end though, she is very happy to see them in a healthy, happy relationship. And secretly vows to run Jekyll/Hyde through if they hurt her in any way