Saber

In equal part, the FPA characters express respect and affection much differently than the Imperials! Mittermeyer and Reuental would never make fun of Reinhard the way Schenkopp and Cazellnu mock Yang. I think Yang would NOT at all be interested in doing the thing that Hilda and Kircheis do where they coddle Reinhard's sensibilities about his own temper. Yang is good at being diplomatic when he wants to be, but would have no interest in Managing Reinhard. I think Yang would openly grumble, poke fun, and passionately argue with Reinhard if they spent enough time together. But I also think Reinhard's huge amounts of respect for Yang make him someone that could throw cold water on Reinhard's tantrums.

When they meet in canon, they're having fun together. Their back-and-forth is quick and challenging to each other in new ways, and I think that could be the basis for a strong friendship or an interesting romantic relationship.

One of my favorite moments in their conversation is when Reinhard tries to goad Yang into selling him on democracy. It reads like he wants Yang to challenge him, and maybe even wants Yang to convince him; to play it out, hypothetically.

But I think where Yang is at in the OVA, he's too exhausted and too heartsick to play with Reinhard in this way. He is not going to try to change the Imperial system from the inside, and I think he's too fond of Reinhard and too upfront in his politics to be anything less than honest in their personal relationship (he will plot against him, but he won't swear loyalty to him and then plot against him).

(lol also I just rewatched the scene where they meet to write this post and WHAT is this exchange:

what is this strange self-effacing reinhard moment lol?? fishing for yang to call him charistmatic?? well, it works because he immediately does)

I think when Bucock say tells Reinhard "Yang would be your friend but never your underling" (paraphrased) that is the key to this. Yang will not, perhaps under any circumstances, do the thing that Kircheis does where he swallows both his deep misgivings with Reinhard's choices and Reinhard telling him to shut up and mind his place and continues having faith in Reinhard. If Reinhard were to be close with Yang in any capacity, he would need to be able to take him as an equal, and I think that would be the central question of their relationship. Is Reinhard capable of that?

(maybe this is the direction they go with Reinhard marrying Hilda! I haven't watched season four yet)

In some ways, it's something that I wish the anime explored in companion to Reinhard's relationship with Kircheis. If, given another chance with another person, perhaps the person he most respects in the whole world, could he do redeem the fatal flaw of his most formative relationship? Could he take someone truly as an equal?

Anyway, that's a lot of rambling to say: I think it depends! I think the thing that most stands in the way of them getting along is Reinhard's carelessness with the lives of others; I think Yang could be amused and even endeared by Reinhard's foibles as long as they don't have a body count. If that makes any sense?

Anyway I leave you with this screenshot of Yang's expression when they meet: