Of all the imprinted couples, Quil seemingly has to wait the longest for his soulmate to mature.
Quil Ateara V
Quil Ateara V was born and raised in La Push. His father, Quil IV, passed away during a storm, and Quil was raised by his grandfather and mother. He had Jacob Black and Embry Call as best friends, but they had a brief fallout when Jacob and Embry phased into wolves.
- "Quil will be the best, kindest big brother any kid ever had. There isn't a toddler on the planet that will be more carefully looked after than that little girl will be. And then, when she's older and needs a friend, he'll be more understanding, trustworthy, and reliable than anyone else she knows. And then, when she's grown up, they'll be as happy as Emily and Sam."
- ―Jacob, on Quil and Claire's relationship.[src]
At some point in the novel, Claire and her sister are brought to their aunt Emily's house for a visit, and Quil came by while they are there. He imprinted on Claire, much to the horror of Emily and the pack. There had been legends about imprinting on children, but they were considered a myth.
The fact that Quil had imprinted on a toddler was shocking, but the pack knew from his thoughts that it wasn't the way it looked; he had strong, but entirely platonic feelings for her. He regarded her as a little sister, nothing more, and the bond between them meant that he would never do anything that he knew might hurt her in any way. In spite of this, the pack knew that from the outside it looked depraved, and to protect both Quil and Claire they kept the imprinting a total secret.
Jacob mentions Quil's and Claire's first encounter to Bella in Eclipse. Given the large gap in their respective age, Emily and Bella find their relationship scandalous and have a hard time not making judgment, but Jacob assures Bella that Quil is simply being an older brother to her, with no romance in mind; and as she grows, they may become a couple and that Quil is not aging for the moment due to his active shape-shifter physiology.
In the middle of Breaking Dawn, Claire has her 3rd birthday party and Quil is invited and Claire got make-up for her birthday which Emily persuaded them to try out on him. After the party, they play at the beach and encounter Jacob.
Jacob tries to persuade Quil to date other girls while Claire is still young, but he finds himself unable to notice other girls now. When Jacob, Seth and Leah first separated from the pack, Quil is only unable to join them because of his ties to Claire, who also seems to be very possessive of him.
Jacob said that he had seen Quil play peek-a-boo for one hour straight without getting bored.
They make a brief appearance together in Breaking Dawn - Part 1 with the rest of the pack at First Beach. Quil and Claire make a short walk down the beach with Jacob, Seth, Leah and Embry watching.