I always thought Jeanne and Francis (particularly with his WW1 costume from APH) really look together, and I really wish there was more Fate x Hetalia crossover fanarts, be they of France and other French Servants like Jeanne Alter, Napoléon or Edmond Dantès, or other countries and their local Servants.
Siegfried always has been one of my FGO MVPs, from the early days of the Orléans Singularity many years ago to the more recent Ordeal Calls, but truth be told, having him face the Dragon of Albion and slay it twice in two epic battles was one of my best memories with him.
That, and of course the rematch/duel against Fafnir in Orléans and having him as my main Servant through the whole Götterdämmerung Lostbelt and seeing him gloriously fell Surtr-Fenrir in the end.
It's a shame there isn't more art of Cú Chulainn with his Prototype self's clothes, he really looks good in them, and I must say I had a blast playing as him wearing those clothes in Extella.
On a side note, it's always good to see art of the Hound of Culann with either one one of his horses or the two of them. Here, we can see him with what I assume to be Liath Macha, his grey steed.
