"I just want to save my friend, okay?" Ashe Ubert and Yuri Leclerc
Yuri was first introduced via the Three Houses DLC, and Cindered Shadows just barely hinted that he and Ashe had some history, or at least were familiar with one another. They have a unique battle quote in chapter 1, Ashe talks to Yuri a bit after the final battle, and Ashe's adoptive father Lonato is a minor lord under Yuri's adoptive father Count Rowe.
Sadly, Three Houses didn't do anything with this beyond Yuri getting battle dialogue with Ashe in Verdant Wind/Silver Snow. No supports, no meal or chore dialogue, nothing. This was incredibly disappointing, but didn't stop fans from shipping it and coming up with all sorts of speculative headcanons. My personal favorite is them being childhood friends.
Then Three Hopes happened. And we finally got the interaction shippers had been craving. It...wasn't what I expected, but I was not the slightest bit disappointed.
In Three Houses, we know Yuri's into some shady deals and dangerous things, but he also has the stable background of the Abyss and later Garreg Mach once you recruit him. He's no angel, does plenty of dirty things to keep his people safe, especially his ailing mother who he loves more than anything.
Ashe, on the other hand, is all about justice and doing good, even though he was a thief in his childhood. In fact, it's made clear he's obsessed with Doing The Right Thing because he's guilty over being a thief. So naturally, he might not approve of Yuri's actions...and their supports make it very clear he doesn't.
In their B support, it's all about the moral angle. Ashe tells Yuri his actions are wrong and Yuri, who does not enjoy being lectured, throws Ashe's own past back in his face. Ashe is shook because he never told Yuri about any of it.
(My feeling is that Count Rowe spilled the beans, because he's kind of a dick.)
So yeah, Yuri wasn't the sweetest guy in Houses, but he's more of a prickly ass in this game, not quite on the level of Houses!Felix but without the stability of the Abyss and the Academy he's more of a tsundere.
Ashe, however, is not giving up on Yuri. Cut to their A support where Yuri's about to be killed, and Ashe shoots the guy before whisking Yuri to safety. This is where it becomes clear it's not just Ashe's strict knightly moral code saying crime is bad.
Yuri tries to do the old "guess what, the world is messy, to make it in this life you've gotta get your hands dirty, I'm proud of it" edgelord routine. Ashe aint having any of that:
The idealistic, righteous, moral knight renders the edgy Lord of the Underworld speechless, and Yuri falls for that "cornball line" like a ton of bricks.
In Azure Gleam, Ashe and Yuri share a paralogue with Catherine, "Love and Hate in Wartime" where Ashe gets attacked by Gaspard remnants who sling blame at him for Lonato's fate. Yuri, Catherine, and Shez come to his rescue and Yuri tells off the jerks when he sees Ashe starting to falter.
(Then of course it turned out Pallardo was manipulating them for money, so they kill him.)
Yuri is his usual overly pragmatic "no one's hands are clean" self, but he still reassures Ashe that he's a good person and he didn't do anything wrong, and that he's still a knight. Then they have some adorable banter because they do that in Three Hopes.
Ashe and Yuri are recruitable in every single path on Three Hopes, so they have training, meal, and chore dialogue along with battle quotes if you have them as adjutants. And there is quite a bit of adorable banter in there, you really get the sense that they're familiar with each other.
Ashe also has dialogue with Yuri in chapter 9 of Azure Gleam, where Yuri is a recruitable enemy, and Yuri has dialogue when the situation is reversed in Golden Wildfire chapter 11. In chapter 12, Yuri questions Claude's plans to attack Fhirdiad, but says if Ashe is okay with it then so is he.
The game still doesn't delve into their past together, so we're still free to headcanon whatever we will. Which I personally am glad for. I will not give up on Ashe and Yuri being childhood friends. (Yes, Yuri refers to Ashe as "Lonato's kid" but he could just be playing it cool.)
During Three Houses, I shipped it based on the minimal dialogue they got and my speculations about their past together, but also because I thought they meshed really well. They were basic foils to one another: two street kids adopted by the nobility in Faerghus, both knew how rough the world could be and had to do terrible things to survive, but while Ashe was adopted by a kind person who treated him well, Yuri did "favors" for a noble to get a roof over his head and his foot in the door at the Officers Academy, which said noble happily took advantage of to keep using Yuri as he pleased. Ashe chose to believe in goodness and become a knight just like the ones in his books and his adoptive father, Yuri kept doing crimes and held a cynical view of the world. Ashe is kind and gentle and optimistic but doesn't take shit from anyone, Yuri is snarky and cynical but is also kind and tries to be a different sort of knight to the people in the Abyss and his ailing mother.
Their personalities developed differently in Three Hopes, but to me this only cemented them being perfect foils and therefore good for each other. Ashe needs to be reminded that even knights have to get their hands dirty, whether it's turning against your homeland or helping to put down your father for his rebellion, while Yuri needs someone to remind him to take care of himself along with everyone else he wants to protect. And the game basically tells us they're good for each other like that, through their supports and their paralogue and their concern for each other. They act like a standard edgelord and boy scout pairing on the surface, but they're so much more, which leads me to my next point.
Going back to their A support: Ashe's insistence on protecting Yuri no matter what is on par with Aang from Avatar: The Last Airbender aggressively refusing to kill Ozai because he won't turn his back on his people's values (or give him the satisfaction of a martyr's death in battle), and how Zuko, who mocked his values a few episodes ago, thought Aang did the right thing because Ozai could stand to learn from his mistakes. Zukaang also happens to be my number-one m/m ship in Avatar and second favorite ship overall.
I've always had a thing for idealistic heroes stunning edgelords into silence, especially if the edgelords fall for them. I also have a thing for grumpy edgelords who think they're so above it all being soft and weak for idealistic cinnamon rolls or naive dorks. Ashe/Yuri in Three Hopes fits that profile perfectly.
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