I think that [parallels between Sam and Castiel] makes Sam more sympathetic towards Cas. You know, Dean seems to be having a hard time forgiving Cas than Sam in general. I think that Sam has been through a lot of similar stuff, and is more forgiving in general.
Sam/Castiel slash fanfiction pairs the characters Sam Winchester and Castiel in a romantic or sexual relationship. A ship with humble beginnings, it continues to grow traction in fandom and gain new shippers daily, particularly on Tumblr, where it enjoys a healthy and substantial life in the form of numerous fanworks and several sassy-exclusive blogs, such as fuckyeah-sassy and sastielweek. Sastiel shippers are fans who appreciate the significant parallel arcs of both characters, and who enjoy imagining them in a relationship, while still remaining respectful of both the actors' personal lives and the characters' network of relationships, unlike other, more zealous shippers. The pairing is also known as Sassy or Sastiel.
Castiel: Hello, Sam.
Sam: Oh my God – er – uh – I didn’t mean to – sorry. It’s an honor, really, I -– I’ve heard a lot about you.[Sam is taken aback]
[they shake hands, Castiel somewhat reluctantly]
Castiel: And I, you. Sam Winchester – the boy with the demon blood. [Castiel takes Sam's hand in both of his, reminiscent of a gesture of comfort] Glad to see you've ceased your extracurricular activities.
From Castiel and Sam's first scene together in 4.07 It's the Great Pumpkin, Sam Winchester, the two have grown into a sort of odd friendship: two characters who were never supposed to be on the same side, fighting with each other and for each other despite their differences. Many of their scenes together, and references to each other, are based in providing comfort, looking after each other's wellbeing, or asking after each other's mental and/or emotional state.
Sam: I need some advice.
Balthazar: Advice?Sam: Cas can't help me. I need to know if there's a spell or a weapon, anything that can keep a soul out -- forever.
Sam: Angel advice.
Balthazar: Well, then go ask your boyfriend.
In 10.05 Fan Fiction, we found out that Sam was rather partial to the pairing himself.
Sam: I don't understand.
Dean: Me neither.Sam: (smirks) No, of course it's not my issue. You know... How about Sastiel ? Samstiel ?
Sam: I mean, shouldn't it be... Deastiel ?
Dean: Really ? That's your issue with this ?
- sastielweek hq: the central hub for many Sassy community projects, such as Sassy Week and Blind Sassy Exchanges
- Sam/Castiel comm on LJ
- Sassy_OTP. A community for all things Sam/Castiel, it delights in Crack. The comm invented the mashup pairing name Sassy.
- Sassy starter kit: a step-by-step guide to the successful shipping of a moose and an angel.