Character Analysis
So, yeah, Marion and Shiva are two separate people—but at the same time, they're kind of not. The boys are born joined at the head and end their lives joined at the liver; in the meantime, they often act as a unit, to such an extent that Marion, the narrator of the novel, sometimes calls himself (themselves?) ShivaMarion.
So what's up with the kinda sorta sometimes-but-not-always conjoined twins?
Once a Twin, Always a Twin
Marion Stone's most important characteristic is that he's really half of a whole. He was born conjoined with his twin brother, Shiva, and even though the boys have been physically separated, surgeons can't seem to sever the spiritual connection they share. Marion is the novel's narrator, but he speaks for both himself and his brother. Check it out:
We—"The Twins"—were famous not just for dressing alike but for sprinting around at breakneck speed, but always in step, a four-legged being that knew only one way to get from A to B. When ShivaMarion was forced to walk, it was with arms locked around each other's shoulders, not really a walk but a trot, champions of the three-legged race before we knew there was such a thing. Seated, we shared a chair, seeing no sense in occupying two. (3.18.4)
The boys behave as a unit, taking on a collective name. That might make it seem as though it's hard to really know either one of them, but it's actually not the case. Each is his own person, though part of each boy is really wrapped up in his brother.
For example, Marion and Shiva are able to communicate without using language. They just sort of know what the other is thinking without having to talk about it. Actually, as a child Shiva doesn't talk to anyone; it's Marion who is in charge of speech. Marion, in fact, says that he "covered for Shiva's silence. I did it unconsciously; if I was talkative to excess, it was because I saw this as the necessary output for ShivaMarion" (3.18.12). So Marion and Shiva are different, but even their differences are due to their connection.
Splitsville
When Marion and Shiva grow up, they also grow apart. One day, when they're sixteen, Marion watches his brother dancing in the dark: "He was taller than I saw myself, and he had the narrow hips and the light tread of a dancer. [...] He looked at me in the mirror, which gave me goose bumps. 'A good time was had by one and all,' he said in a hoarse voice that I didn't recognize" (3.32.61-63). The boys are like mirrors for one another, but this mirror is starting to shift.
The voice, which the boys used to share (since it was only Marion who did the talking), is now unrecognizable. That's a sign that Marion and Shiva are beginning to have their own thoughts, desires, and voices. But even their split turns out to revolve around the same desires: Marion loves Genet and wants to marry her, and for a while, he thinks everything is hunky-dory: "My brother loved me, he loved Genet, and I loved them both" (3.33.94). Unfortunately, this love triangle doesn't have happy results.
Marion wants to wait until he's married to Genet to have sex with her, but Genet is ready for it now. And she doesn't wait: she has sex with Shiva instead. Marion discovers this when Rosina, Genet's mother, comes screaming at him as a result of the fact that she thinks he's the one who took her daughter's virginity:
But I could smell blood, the scent of Genet… and I could smell semen. It was mine. I recognized my starchy scent. No one else shared that odor.
No one but my twin brother. (3.34.67-68)
The graphic description of the post-sex smells shows us how the twins' connection is never-ending. Marion isn't even able to tell apart his scent and his brother's; it's as though he were the one who had deflowered Genet. Everyone treats him as though he were the one, and he even acts as if he were, too. It's like the fact that they're two different people doesn't matter.
Except that it does. Marion says that he "could have killed Shiva that night" (3.34.70). He also moves into a different room to be away from his brother: "It would be the first time in our lives that we did not occupy the same bed. If there were filaments and cords of yolk or flesh that kept our divided egg sticking together, I was taking a scalpel to them" (3.34.79). So because they are the same person, wanting the same things, the boys finally split into two.
Together Again
After this split, things are never really the same—until Ghosh dies. With their adoptive father in terrible shape, Marion "decided to leave Ghosh's old bungalow and return to the bed I used to share with Shiva. I convinced Shiva not to sleep on the floor in the corridor. We slept awkwardly, on the edges of the mattress, getting up several times in the night to check on Ghosh. By morning, our heads were touching" (3.36.73). Grief puts the boys back in something like their old position.
Tragedy will continue to be the uniting force for the twins. When Marion is sick and in a coma, Shiva volunteers a piece of his own liver for the transplant the will save his brother. He explains to the doctors, "'A perfect match is what you would have if you took the liver from me […] His body would see it as self, not as foreign in any way'" (4.51.103). The boys' bodies can be considered one body, even though they're walking around separately, because of their DNA match.
Unfortunately, Shiva dies from complications after the surgery, and Marion feels as though he has died, too: "I felt physically vulnerable in a way I'd never felt when we were a continent apart, as if with his death my own biology was now altered. The heat was rapidly leaving his body" (4.52.87). This seems like a great tragedy, until Marion realizes that it's actually just the twins returning to their natural state of togetherness.
Marion starts to see these events as "a brilliant and daring rearrangement of organs" by which "ShivaMarion had readjusted" (4.52.96). He breaks it down for us:
Okay—just about everything on his side died, but we retained half his liver, which was thriving. What we had to do now was economize further, go halves again, tough measures for tough times: two legs sufficed, so also with eyes, kidneys. We'd go with half a liver, one heart, one pancreas, two arms…but we were still ShivaMarion.
Shiva lives in me. (4.52.96-97)
The character of ShivaMarion, which has been split throughout the novel from the time the twins were born up until the transplant, is now one again. In fact, the narrator briefly adopts the first-person plural (that's "we," for those of you watching at home) rather than the singular (or "I") to signify this union:
"Here we are," I said.
She came into my arms.
We held her tight. (4.52.106-08)
Marion and Shiva Stone's Timeline