Smorgasbord
"Smorgasbord" may not technically be a certified descriptor for an author's narrative technique, but there's really no other way to describe this book. Natasha and Daniel's chapters are each narrated in a traditional first-person point of view, switching from Natasha's voice to Daniel's voice as necessary. There's also one random first-person chapter toward the end that's written in Samuel Kingsley's voice.
Beyond that, the chapters about the peripheral characters are written in a "third-person limited" voice: We're still inside one character's head, but they're addressed by their names like somebody else is telling the story. It's the difference between "Jeremy can't forget about his conversation with Daniel" (third-person limited) and "I can't forget about my conversation with Daniel" (first person).
Finally, just for kicks, Yoon throws in background information about everything from evolution and half-lives to Charlie's future and the Greek sisters of Fate. All of these chapters are written in "third-person omniscient" voice—no characters involved, just an all-seeing, all-knowing voice. In a book that tackles so many deep conversations about spirituality, some people might see these chapters as the voice of "God" in the novel.
Switching narrative techniques may not seem like that big of a deal, but it's a shrewd move by Yoon. She keeps the reader most connected to the stories of Natasha and Daniel, but she also allows other characters in the story to have their own, separate moments in the spotlight.