Over the past few weeks, gamers in China have become obsessed with a free-roaming Japanese frog.
Travel Frog has topped the charts of free game category in Apple's App Store in China for more than a fortnight.
The game, developed by Japanese company Hit-Point and originally called Tabikaeru, is only in Japanese, but is easy to play despite the language barrier.
It lets players own a cute little green frog which lives in a hut, where it eats, writes, reads and sharpens pencil - sometimes it dozes over books.
Out in its garden, player can collect clover, the primary currency in the game. You collect 20 clovers once every three hours simply by swiping across the garden, or you buy them with real money if you are too impatient to wait for them to grow.
But the most curious feature of the app is that beyond that, players have very little control of the frog. It will frequently leave its home and travel around Japan on a whim.
Players never know when the frog sets off, when it will get back or what it will bring on its return. Sometimes the frog goes home within a few hours; sometimes it could be gone for as long as four days.
It might send postcards, clovers, souvenirs - or might do absolutely nothing for its owner.
There is no way for the owner to control or interact with the frog.
The only thing that players can do is to prepare food, tools and amulets for the wandering frog.
Taste of parenthood
"I like the game because the frog does whatever it likes and I don't have to spend a lot of energy on it." 27-year-old Shen told the BBC.
Xian told the BBC she became a frog keeper a week ago, when she saw her friends share photos on WeChat, the Chinese equivalent of Facebook.
"I check my frog almost every 10 minutes at work, because my job is boring. I marvel at the photos that it sends to me from its adventures," said the 25-year-old.
"My mother longs for my return home when I am away, but she wants me to go out when I am home. That's my exact feeling towards my frog," Xian said.
"But I feel desperate when I keep receiving photos of itself: it is so antisocial and doesn't make friends!
"Today, it posed together with a rat, I almost cried with joy, it finally has friends!" Xian said.
According to the latest data obtained by the BBC, via US-based App Annie, Travel Frog has been downloaded more than 3.9 million times in Apple's App Store in China since its launch in December.
Chinese players have spent more than $2m on in-app purchases for their frog babies.
In Japan, however, it's been downloaded a mere 400,000 times on the App Store and Google Play combined, with users spending only $100,000.
So what's the appeal?
"It really suits the post-90s generation, because we are overwhelmed with work," said Shen.
When he saw the game going viral on Weibo, the Chinese equivalent of Twitter, he downloaded it instantly and now checks his phone frequently for frog updates.
"Every time I open it, I am full of expectations. I want to know whether my frog is travelling, and what photos it has sent to me. I feel it is my son."
When the frog is travelling, Shen finds another way to kill time.
He has created a WeChat group called "Post-90s Empty Nester Huddle Together for Warmth". Young people share feelings of parenthood in the group, to while away their frogless hours.
The People's Daily, the Communist Party's mouthpiece has used it as a chance to encourage "core values" by urging young people to visit their parents more.
"The travelling frog is like everyone away from home," it posted on Weibo.
"What's the feeling of waiting for your kid? Please remember to visit your parents, all wandering frogs."