#Cas went from seeing Sam as an abomination to considering him a friend he'd kill his own siblings for in like a season

[thegracefallen]

@ruinedmyself

"He resisted Michael. Maybe you could resist Lucifer." ↳ 5.21 - TWO MINUTES TO MIDNIGHT

[marlborosam]

(Apologies for how long this reply is- I hope you don't mind!)

I would say personally that the appeal of SamCas is because of the ways Cas's relationship with Sam is so different than with Dean! Sure, they may have gotten off to a bit of a rocky start when they first met, and they don't get as much screentime or as many interactions, but the moments we do see them share later on mainly revolve around themes of support and faith in one another as well as showing that they're comfortable in each other's presence.

Right from their first meeting in S4, Sam is absolutely starstruck. This is a person who prays every day, and who believes in angels, and considers himself to be a faithful man. This is the Heavenly body that he's been praying to, and he's suddenly come face to face with the divine. And when Cas says "the boy with the demon blood" there is no real malice or scolding in his tone- he is simply stating what he knows. It's immediately followed by "I'm glad to see you've ceased your extracurricular activities," which to me is not an altogether aggressive statement, since this first meeting involves Cas knowing that Sam is an "abomination" and still choosing to shake his hand and then to tenderly cradle Sam's hand in both of his own. He is willing to look into his eyes and touch what Heaven has condemned.

There are moments in earlier seasons where they show a protectiveness towards each other like: "You are not taking Sam Winchester. I won't let you." to Lucifer, "You come near Sam Winchester and I'll kill you." to Anna, and "Look, Cas is our friend, and I'd die for him, I would..." These moments are a little sparse but nonetheless important to show the bond that begins to develop over the course of S4-5. One significant moment in those seasons is when Sam uses his powers to kill Alistair and tells Cas that the demons aren't the ones who are killing angels, that something else is killing his soldiers, and Cas believes him. He takes Sam's word for it when he goes to Uriel next. "Maybe the killings aren't demonic. Sam Winchester says the demons have nothing to do with it."

When the Apocalypse is diverted, Cas reveals near the end of S6 that he was the one who rescued Sam from the Cage (or so he'd thought at the time, since leaving behind Sam's soul was an accident).

Cas: We won... we stopped Armageddon... but at a terrible cost. So I knew what I had to do next. Once again, I went to harrow Hell to free Sam from Lucifer's Cage. It was nearly impossible, but I was so full of confidence, and mission, but I see now that it was arrogance.

I've seen people say that he saved Sam for Dean's sake so he could get his brother back, and I have no doubt that in some way that was probably part of his motivation. That was not the only reason for making this rescue, though. Cas, of his own personal opinion, considered losing Sam to be a terrible cost, and without telling Dean took it upon himself to save Sam. When he first raised Dean from Hell, he hadn't met the brothers yet, and thus was acting only on Heaven's orders, and it took a group of angels to raise Dean. Cas knew the Winchesters by the time Sam jumped, and he considered them friends, and he couldn't stand the idea of losing his friend, so he singlehandedly braced going to the Cage to save Sam within days of him jumping. And he brought Sam to where Dean was staying with Ben and Lisa, but when Sam chose not to return to him and make his presence known, Cas doesn't push it or tell Dean anyway. He leaves this as a choice for Sam to make, and he respects that decision.

When the boys are beginning to suspect that Cas may be hiding something, Bobby uses the phrase "Superman going darkside". Dean then proceeds to give Sam a Look while saying "This makes you Lois Lane." Just a moment I thought I'd point out, lmao.

At the beginning of S7, when Dean has lost hope that Cas can be saved, Sam is afraid and doubtful, but he wants to have faith in his friend. So he goes outside and prays.

Sam: Hey, Castiel. Um... Maybe this is pointless. Look... I don't know if any part of you even cares, but, um, I still think you're one of us, deep down. I mean, way, way, way off the reservation, but... Look, we still have till dawn to stop this. Let us help. Please.

And Born Again Identity... Cas breaks down Sam's mental wall over the course of the Godstiel arc, and when he gets his memories back and he and Dean come to see Sam at the hospital, he feels a very deep sorrow and regret over the pain he's caused his friend. And you know what he decides to do? He takes on the worst of Sam's Hell trauma in order to save him, at the cost of his own sanity. "And if I can't tell you again...I'm sorry I ever did this to you."

Later in S7 the moment that sticks out to me the most is the conversation where Cas tells Sam that "I was lost until I took on your pain." He does not regret his decision. He wanted to do whatever he could to help make things right.

There isn't much in S8, but their "Agent." / "Agent." interaction and Sam's smile when Cas says "Cas is back in town!" are both incredibly endearing moments! They're comfortable with each other, and they can have fun and find humor in the things that they do together.

S9 is where one of the most significant moments in the development of their relationship occurs, I think. In First Born, when Sam urges Cas to complete the grace extraction so they can find Gadreel, even if it's at the cost of his own life, Cas vehemently tells him, "I want to find Gadreel as much as you. But nothing is worse losing you." This episode also has some moments between them that are lighthearted and playful, like sharing a PB&J while Cas laments no longer being able to enjoy the taste and "You have a guinea pig? Where?" / "I'm the guinea pig." / "...Oh." and:

Cas: Sam, may I ask you a question?

Sam: [jokingly] You just did.

Cas: Can I ask you another question?

Sam: Well, technically, you -- yeah, go ahead. What's up?

There are more moments throughout the rest of the series (14x15 Peace of Mind in particular is pretty popular for Sastiel screentime), but this has already gotten really long so I figured I'd stop here! Sorry this was so long, but I hope it gives you an idea as to what Sastiel shippers like about their dynamic so much!

I say this with 0 hate in my heart 1000% curiosity. Where do Sam and Cas shippers get that vibe from? I only ask bc the main thing that rings true about dean and cas for me is the way that cas’s relationship with dean is so diffrent than his with Sam. I’m curious