Smartphone app services to timid Asian lovers and has record a million downloads ever since its launch last November. Its developers are looking out to new markets.
Couples unwilling to share their relationship with the world through Facebook or other social media have flocked to sign up for Between, an intimate app designed for two.
"Imagine how stressful it would be if your boss followed you on Twitter, or parents added you on Facebook ... Between is the new solution for such pressure," one of the South Korean developers, Park Jae-Uk, told AFP in an interview.
Between, available on iPhones and Android-equipped models, offers privacy for couples who want to swap photos, messages, schedules and short voice messages via smartphone.
Developers say some 4.6 million messages and 350,000 pictures are exchanged daily. Between was named Best Mobile App of the year at a competition for new global ventures in the Dutch city of Amsterdam.
"Facebook and Twitter may do a good job in connecting people in all sorts of ways, but we thought maybe some people want a closed and private relationship," said Park, whose VCNC company runs the app.
"So we turned our eyes to unmarried couples who need such a private relationship platform more than any other groups."
Between lets them share photo timelines, send messages and mark anniversaries, birthdays and other dates on each other's calendars.
Connection to the service is completed when both parties enter each other's phone numbers after registering. If a couple breaks up, one of them may disconnect the service and all the data will be deleted.
"No matter how hard you try to conceal information on other social networking services, it still seems like they are wide open...so we decided to base our appeal on how tightly closed and protected our service is," said Park.
The application is password-protected and is never available to more than two people at any one time.
Between is available in 13 languages including Korean, English and Japanese. At present it mainly targets Asian users because of their culture of keeping loving relationships to themselves.
Some 75 percent of users are Koreans, 7 percent Chinese and 6 percent Japanese.
"I take a lot of photographs with my boyfriend and needed an exclusive space to share them by phone," said 23-year-old Hong Jee-Won.
Another user, Jun So-Min, said Facebook "is way too public, so to keep a record of private content like photos and messages, I use Between. It serves its purpose well and I'm satisfied with it."
Park is now looking for growth in Europe and the United States by tailoring the service.
"The culture is a little different in Europe and the US, so we will try to cater to long-distance couples or engaged couples getting ready for marriage," he said.
Currently, 79 percent of Between users are single and 96 percent of all users are in their 20s to mid-30s.
"Between in a way represents a commitment made by couples, so we rarely see teenagers using the service...their relationship usually doesn't last long enough to take full advantage of it," said Park.
That is why VCNC's engineers plan to develop a system which backs up data for up to one month after a breakup, just in case lovers decide to reunite and reopen their accounts.
"Think of it as an adjustment period for couples," said Park, adding users quite often complain when data is wiped under the current system.
VCNC is also looking for business models from next quarter, such as advertisements and promotions related to couples such as tour agencies, flower shops and wedding stores.
The company currently relies on a one billion won ($880,312) investment made by SoftBank last year and has not yet reported profits.
"Seeing two copycats already showing up on the market, I am sure the couple-related business has great potential, because people become less hesitant to open their wallets when it comes to their lovers," said Park.
"Even though differences might exist between cultures, I believe love is universal anywhere in the world -- and that's what makes Between possible."