Watch: How couples in South Korea show their love for one another
In a country where public displays of affection are still frowned upon, South Korean couples often advertise their relationship by wearing matching outfits - whether socks, shirts, jackets or, more privately, underwear.
It's especially popular with newlyweds, making South Korean honeymooners easy to spot on Southeast Asian beaches in their twinned T-shirts or shorts and "couple flip-flops".
The fashion can also be seen among young people in China and Japan, but South Koreans have taken it to a different level.
The trend has spawned a small cottage industry, with specialist online stores offering "couple swimwear" for the summer holidays, "couple snowboarding suits" for the winter and "couple tracksuits" for those who like jogging together.
Newspapers and magazines churn out stories on how best to pull off the "couple look" with each season's latest outfits.
Eric Kim, a 28-year-old Seoul office worker, said: "When I was in college, I bought 'couple hoodies' with my ex. It felt cool and sweet that we hung out together wearing the same hoodies.
"Also we can show off that we are a couple, not one of those lonely singles."
Older now and mixing with friends who find donning head-to-toe identical outfits as "tacky and embarrassing", Kim says he and his current girlfriend make do with wearing matching shoes.
There is no marketing data on how many South Korean couples go in for matching fashion, but business seems to be booming.
A quick search of keo-peul-look ("couple look") on major Korean internet portals yields a seemingly endless list of online stores selling couples' outfits.
Matching underwear and pyjamas are also popular, typically in pink for women and blue or black for men - but also in a leopard-skin design for both.
Baek Eun-Joo is a big fan of the "couple look" and has a wardrobe of matching his-and-her patterns. "My husband and I have been wearing couple clothes for eight years. We just can't get enough of it," Baek said.
Rather than ridicule, Baek said she was complimented by friends, who asked where they could find the same outfits.
Convinced there was substantial market, she and her husband started an online store called Ggumddakji - a slang term for an inseparable couple.
"It feels weird and sweet at the same time ... and is a great way to reaffirm your love with your partner," Baek said of the trend.
"Plus, South Koreans want to show off things they are proud of, including their relationships."
But the shop doesn't give advice on what couples should do with their outfits if the relationship breaks up.