Ok, the second part of my rambles or why hugging Knives should be considered a form of convention weapon and must be used as often as possible.
A little disclaimer: what I'm gonna to talk about is applied mostly to Stampede and manga Knives. Not so much to 98, because while, objectively speaking, there is no reason for it, I kind of have a feeling that other two would very like to punch him to a pulp. The guy has an incredibly punchable face.
Now, a question. Does Vash love Knives?
Yes, of course. Despite everything Knives did, Vash still consider him his brother and wants them to put away their difference.
Next question: Does Knives feel this love? Or, maybe, I'll paraphrase a bit: does he believe in it?
And here things become tricky. Because yeah, at some level Knives knows that Vash loves him. His little brother is a kind creature, after all, that's ready to share his heart with the whole world. He wants to save humans, wants to save Plants, why not to want to save Knives too, in this mix?
The problem is, Vash, bless his heart and everything, is a damn hypocrite. He gives promises that he isn't able to keep, runs from places to places doing essentially nothing and always, always, always, puts humans first.
So yeah, he loves Knives. Just as he loves his sisters, or maybe worms on this planet. As long as humans are safe, Vash is ready to feel sorry for them, or maybe even ask for forgiveness for everything humans put them through. They'll become better, one day.
And the worst part? Knives isn't exactly wrong in his assessment. Because Vash does put humans first, Stampede especially. And although a big part of the reason for that comes from his guilt complex and well, Knives, maybe you should have thought it a little better before putting it on your brother, but the fact stays: between a Plant and a human, Vash will instinctively choose a human.
Now, let's talk about the aftermath of Tessla's case. Stampede very suspiciously omitted most part of it, showing only Knives' choice of Vash's memories (and keep in mind that the whole point of that showcase was to break Vash, so Knives' "confession" of his motivations can't be taken at face value) and I will die on the hill that in the second season we're going to get Knives' round of it, but for now, let's go with the manga.
We know how it did go: while Vash had his emotional breakdown, Knives fell into coma. It isn't clear, did he faked his amnesia or not but even he didn't, the subconscious trauma still stayed.
And the first thing he saw after waking up? Vash and Rem, laughing together.
Think about this. Vash saw the extent of Knives shock, watching his brother being comatose for days. Even though he wasn't conscious, Vash had an affirmation that his twin shares his grief. Knives, though? He didn't have a chance to see Vash's resentment, desperation and anger. For him, his brother just... Brushed it off. Made a peace with it. And even if the wording was different, even if he was told something like "I understand if you're angry" - Knives already lost his affirmation. He had no chance of showing his anger, not when his twin was so calm about the matter and obviously decided to stay at humans side.
For Knives, Vash has already abandoned him for humans. Forgiveness is a thing that exist for sake of a victim, not a perpetrator, but Vash has already forgave theirs, therefore forcibly dragging Knives along before he even really started to proceed everything.
And so, Knives acted as he, with this mental block, was allowed to:
... And you know the reason of the story.
And after that? Constant arguing about how they should forgive and accept humans. (For manga, it's after the Fall, but in Stampede it started already on the ship. I'm sure that Knives read Bible before, just like he watched war movies before in manga. But after Tessla, he started to see evil there). Open expressions of fury, fear and hate from somebody who is never bothered to even become a bit angry on their sisters' behalf. A gun in your face after you saved his life.
Yeah, Vash's feeling are much more complicated than that. Alas, Knives doesn't have much chance to see that. From his point of view, Vash is ready to forgive humans everything, but Knives? He gets a gun and speeches how they all should live in peace. With a great plan mostly consisting of Plants forgivinig humans until they become better.
So, at some point Knives just... stops listening. He already knows what his brother thinks about him. It doesn't matter. Knives won't let Vash's hate stop his love for him. Gunshots, Vash's cries of anger, pain, fear - it all become a white noise that should be ignored.
Ignore when they hurt you, just do your thing and come to them again and again, and one day they will listen to you? Ironically, but for most part, it's exactly how Knives tries to act with Vash. Well, in his own, a bit psychotic, version of things, with him not only waiting but also taking some actions. (Ok, a lot of actions.)
And it's incredible how all that cold and collected persona dissipates on 12 ep of Stampede, where Knives is left with nothing but a desperation to make his brother understand. Only for Vash, when Knives lays his heart bare, to reject him. Again.
And Vash has his own reasons. Completely understandable reasons, I would say, because while he is a superhuman only in physical sense on things. He had his own anger, and pain, and fear, and inner struggle. Knives hurt him enormously and there is no wonder that Vash doesn't want to give up his stance. And he shouldn't, really. But...
Knives isn't strong, at least, mentally. He created this illusion of being the older, the one in charge, to protect himself (in Stampede, this illusion starts a bit earlier, with him being the "perfect Independent" who for some reason should hide his powers and "weak" Vash, who is, by Rem's words, "perfect as he is") but in the end this made-up hierarchy harmed both him and Vash, locking them in their respective positions. And Knives was motivated by fear, he wanted protection, wanted Vash to stand up for him - something what Vash, who for so many years saw Knives as the strongest one, the one who decides, the one who must be defeated, wasn't capable to do and had no idea about. He had his own personal growth to do, and couldn't be the mentally senior figure Knives needed.
And that's why one day I going to write this fic about TriMax Vash finding himself in Stampede world. These idiots clearly need an older brother.
For Knives, Vash was the one who abandoned him, again, again and again. The one who blabbed about love and peace while aiming a gun at him. For over hundred years, there was only one case when Vash prioritized Knives over everything else, took his side clearly enough that there were no ways left for Knives to doubt it.
And guess what? This single act snapped Knives out his frenzy better that all these bullets before that.
And I'm quite sure that Stampede plot could be quite shorter if upon that meeting five years after the Fall, Vash would confirmed that yes, he understood Knives' ire before confronting him over humans death. Like, the kid was one hug away from breaking down. Too bad that he never allowed himself acknowledge it.
So, the moral of the story: hug your Kniveses. Be cautious, though, because while Vashes bite, Kniveses... Let's say that they aren't very good for your extremities. Assert your dominance with care and don't force them to bottle up their anger, even unintentionally. If you do it right, everything will be fine.
... Well, maybe. Hope for the best, one day it surely will be alright.