David and Nate are at the center of the show, and at the center of their family. On the fringe, in her mind and in reality, is Claire. Nate is 18 years older than Claire—he left home when she was still a baby, and has been, at best, a long-distance brother since. Their relationship has all the trappings of siblings who live far away: a few inside jokes/memories, awkwardness and resentment. Nate, as the eldest, tries to discipline Claire and impart sage advice to her, but she sees right through his act—he was a fuck up, like she is, and has no real advice to give because for all his confidence, he still doesn’t have it all figured out.
Perhaps because they are so similar, Nate and Claire never really forge the relationship that could have been. Claire and David on the other hand, have a much more complicated and, eventually, deep relationship. David never really left home, and so he and Claire seemingly know each other much better when we first encounter them. Or, at least, they have a passable understanding of who the other one is. David thinks Claire is a drama queen and a hormonal teenager, and Claire thinks David has a stick up his ass.
Over time, David and Claire forge an unlikely bond; David becomes, without trying, the surrogate father Nate pushes to be. When Claire gets kicked off of a camping trip for school, she gives David’s cell number to the instructor and the instructor assumes this “Mr. Fisher” is her father. David never blows Claire’s cover; he sees that she has gotten something valuable from this experience, and lets her get away with it. David, to his credit, never really talks down the Claire—he doesn’t necessarily confide in her or lean on her for support the way he does with Nate, but he treats her as an adult and an equal long before anyone else in the family does.
Lisa’s disappearance is another defining moment in the Fisher family. Nate is understandably devastated by his wife going missing, and both David and Claire offer their fullest support for him. The clearest example of this is when Nate travels to where Lisa’s car was found and spends a night in a cheap motel room. He gets a knock on his door and opens it to David and Claire, there to do whatever they can for him. If we compare this to not even two years earlier when Nate and David don’t even share an embrace at the death of their father, we see how far they have come.
The scariest, most disturbing episode of Six Feet Under is “That’s My Dog” (S4:5), where David tries to do what he thinks is the right thing by picking up a hitchhiker. The hitcher turns out to be a drug-addled maniac , who kidnaps David on an incredibly scary and dangerous journey around Los Angeles. He forces David to smoke crack, abandon a body, sticks a gun put in his mouth, and pours gasoline on him with the intention of burning David to death. It is, needless to say, a harrowing experience (and one of the most polarizing episodes of the show), shaking David to his very core.
David turns to Claire, who catches him having a panic attack at a viewing of a young man who was murdered, and explains to her the events of that night. Nate, at this point has walked away from the family business after Lisa’s death, is urged to return by Claire. She knows that David’s responsibilities and stress would both decrease a lot if Nate would come back to help. Nate is reluctant, but Claire pushes him: “You know he would do it for you”. And with those words, Nate acts completely against his self-interest, and returns to the business he never wanted to help his brother.
Late in Season Five, Nate suffers another seizure as a result of his AVM and winds up in a coma. Ruth is camping without a cell phone, and so it is up to the Fisher siblings to take care of this crisis themselves. Because of Ruth’s absence, and Nate’s disintegrating relationship with wife Brenda, David and Claire wind up being the people who spend the most time with their brother when he awakes from his coma. Claire, who has been in a weird headspace all season, finally starts acting like an adult; she is assertive, concerned, and caring, almost motherly, in the absence of Ruth.
David continues his ascent to the head of the Fisher family by running interference between Benda and Maggie (a former-step sibling who acts as the catalyst for Nate’s final rejection of Brenda and final embrace of spirituality), being the calming, stabilizing force at the hospital, and the selfless brother, sitting vigil by his brother. It is while sitting with his brother that the two of them experience a shared dream; father Nathaniel Sr. driving the van with a Shaggy-esque David and a normal Nate to the beach. Nate, on the beach, looks at the ocean and says “I’m going in!” Nate runs into the water, and when David awakes, Nate has died.
Nate’s death devastates Claire and David. Claire spirals into an alcoholic stupor and nearly destroys both her relationship with then boyfriend Ted and her future. David is once again visited by images of his attacker, and his grief brings him to a place where he cannot be an effective father to his adopted sons, so David returns home to the Fisher house temporarily.
However, it is David’s grief and his working through it that leads he and Keith to buy Rico and Brenda out of Fisher and Diaz—once again, it is Fisher and Sons. It is also the bravery that Nate exhibited in leaving home at an early age that inspires Claire to move to New York, even if the job she had lined up falls through. Just as his return home brought the Fishers together, his leaving them sets them on their paths they will follow for the rest of their lives.
In many ways, David and Nate are their parents. Nate is his father—distant, hates his job, and needs to escape occasionally. David is his mother—his life isn’t exactly what he wants, but he tackles it the best he can, while trying to be everything to everyone. Claire is a little bit of each parent and, more evidently, a little bit of each sibling. Yes, she leaves, but because of a good reason—she is embarking on a career, unlike Nate, who just wanted to get away. Claire dedicates herself to her work—art and photography—the way David does, and seems to have a similar work ethic to her brother.
Continuing the Fisher family, both Nate and David have children of their own—a pair each. Nate’s children have two different mothers and both grow up without him, continuing Nate’s theme of not being there for his family. David’s children are adopted, but eventually see him as their true father; a shelter from the storm of life. Claire never has children; she once again has to break the patterns her brothers set out for her and forge her own path.
In so many other shows, the three disparate siblings from the pilot would be as close as could be by series end; Six Feet Under didn’t do that. Yes, they have grown closer, but Claire, David and Nate are still messed up, awkward, unsure people who don’t completely get their siblings.