"They get jealous and even fight a lot, but they always come back and make up," she says of the show's main characters.
Guo spent much of her childhood alone, watching television and talking to dolls and plush animals, none of which, she says, made up for not having a brother or sister.
Now a professional illustrator, she's turned her childhood experiences under China's one-child policy into what the New York Times deemed one of the best picture books of 2015.
"The Only Child" shows the dreamy, wordless adventures of a little girl as she makes her way to her grandma's house after being left at home by busy parents.
"I feel sad for the missing part when I share the experience with people who have brothers and sisters," says Guo, who's now based in Singapore.
Growing up, Guo, like others of her generation, thought little about what having a brother or sister meant. She had no comparisons to draw from her only child friends.
"I always had the TV on the whole day," Guo recalled.
"Later I realized it's just because I wanted someone to talk with in the empty room so that I didn't feel lonely."
China's strict birth planning policies, which were eased last year after three decades
, meant that a majority of Chinese families were restricted to having just one child -- especially in big cities.
Those that fell pregnant without official approval faced eye-watering fines
and, in millions of cases each year, women were forced to undergo abortions
Years later, however, as China's only children have grown into adults, started their own families and been exposed to diverse family structures elsewhere through living and traveling abroad, Guo and others like her are exploring the sibling relationship that they never had through art.
Li Tianbing, a critically-acclaimed Chinese painter based in Los Angeles, has also reflected on his lonely childhood in recent years.
"I took up painting only to endure the seemingly endless time being alone," he said.
Based on five old photographs of himself, Li re-creates his own portraits stroke by stroke, but also adds imaginary brothers.
His playmates, along with toys, books and bags, are splashed with ultra-bright pigments, while his image is rendered in nostalgic black and white, creating a surrealist feel.
As a grown up he could do nothing about the reality, but by creating imaginary siblings on canvas, he feels like he could find "someone for company" and also be "at peace with his childhood loneliness."
"As I paint, my memories rewind as though I was rewriting my childhood diary," Li says. "Painting has a healing power."
Li says his work isn't political and describes it as "voluntary and purely personal." But he hopes his paintings will shed light on the far-reaching impact of China's birth control policies
Guo's book will be published in China later this year.
Of course, being an only child isn't unique to China and loneliness is universal -- making their work appeal to a global audience.
Isabel Atherton, director of agency Creative Authors and Guo's agent, is one of them. She said she immediately connected with Guo's book and recommended it to publishers.
"Despite having a brother myself, I identified strongly with the child in the book," she said.