At the time, Ko was unhappy working as a designer for a famous brand, where she had a very busy schedule.
"My life was crazy then. Every month we needed to come out with 150 different designs for production. Every year, there were 14 collections," she says. "There was no time to sit down and discuss things in a creative way."
It was during what she calls the "lowest period in her life" that she came up with a colourful way of dealing with her sadness: creating a "friend" called la petite mu mu.
The character, which she first drew on a computer, brought light into a dark place. "She was my emotional outlet. I wasn't able to communicate with others, but I could with mu mu, who is very supportive," Ko says.
Through the stories and images that Ko created, mu mu virtually "came to life", easing the unhappiness of her stressful life. "There were days when I worked until 5am, went home to take a quick shower, changed my clothes, then headed back to work again," Ko recalls. "I kept asking myself: where is the creativity? Is this the kind of life I want?"
A fashion designer by training, she was designing, travelling overseas and making sure production happened on time - but this was not the life she had in mind when she was studying at the Surrey Institute of Art & Design in Britain and Hong Kong Polytechnic University.
Ko soon became depressed and sought help. "My doctor told me to prepare for a very long recovery."
In 2007, she had to quit her job to rest at home. "I didn't want to rely on medication, so I started to look for [natural] ways to lift my mood," she says. "I took up something I've always enjoyed - drawing."
As she drew, a female character emerged.
"Mu mu is a four-year-old girl. She never grows up. Often I see her alone in her secret garden," Ko says.
Ko could see herself in mu mu, whose image she now portrays in paintings, sketches and other media. Later, a fellow artist created a 3D model of mu mu.
Ko has created many tales about mu mu, some of which are to be featured in a new illustrated book she plans to launch in December.
"One story is about her fear of thunderstorms ... One day, mu mu got tired of being afraid so she turned herself into a Thunder Rabbit. She decided to face her fear head-on," Ko says. "Every one of us has something we're afraid of. The fear will come back again and again until we face it."
Ko has a more positive outlook on life now, and has been working again over the past few years. Looking back, Ko is grateful for the lessons she learned from her dark days.
"Sometimes we have to learn to let go of things that aren't suitable for us and walk away from situations that are stressful. Creativity will only happen when we are in a relaxed state of mind," she says.
"There is always a way out to any problem. You just have to believe in yourself. Always keep a playful heart and a 'Thunder Rabbit' spirit."
Fion Ko's art is on display until April 15 in the Easter Dream Garden exhibition at the World Trade Centre in Causeway Bay