Actors Ryu Jun-yeol and Han So-hee, newly announced lovebirds in the South Korean entertainment scene, recently vowed legal action against a barrage of what they say are malicious comments targeting their romance. In just three months, Han in particular went from being voted "female celebrity most people want to spend Christmas with" to losing endorsement deals.

The mere accusation of "hwanseung yeonae" -- which roughly translates to "transferring between dating partners" -- can be damaging to celebrities whose careers depend on the public's affection for them. It was recently reported that Lotte Chilsung Beverage did not renew its marketing partnership with Han after it expired this month, and Nonghyup Bank did the same.

Secondhand car sales platform Hey Dealer closed the comment section of its YouTube ad featuring the actor due to malicious comments against her.

Fallout concerning Ryu -- the man at the center accused of the "quick transfer" -- has yet to significantly materialize beyond harsh online comments. It was reported Wednesday that multiple supporters of Greenpeace Korea have requested the organization drop him as an official ambassador. Greenpeace Korea told local daily Kukmin Ilbo that it is looking into the requests, adding it would "do our best to find better ways to promote our campaigns.”

Yet by nearly all indications, the love life of former media darling Han has led to her suddenly falling out of the public's favor.

Actors embroiled in controversy

Hwanseung yeonae is loosely defined among South Koreans as moving on from one romantic partner to another with no or minimal time between the relationships, likening the act to transferring between buses or subway trains on one's daily commute. The relatively short period between Ryu's relationship with Han and the termination of his prior relationship with singer and actor Hyeri, reported in November, resulted in the new couple being suspected of the detested form of dating.

Last week, Han and Ryu were reported to be spotted at a hotel in Hawaii together, leading them to promptly admit to being in a romantic relationship. But reports have since showed that the two had been acquainted since November of last year, around the same time Ryu was reported to have ended his seven-year relationship with Hyeri.

Upon reports of her ex-boyfriend's new girlfriend, Hyeri unfollowed Ryu on Instagram and cryptically wrote "That's funny" on her page. Han then apparently responded on her own Instagram page, "That's funny, for me too," saying she does not fall for anyone who is dating someone else. Both posts have since been removed.

Upon public scrutiny that followed, Han issued an official statement saying that she started dating Ryu early this year, and his relationship with Hyeri had actually ended early last year. She urged the public not to use the word "hwanseung," admitting that she was irked by the accusation.

On Monday, Hyeri wrote in an official statement that she and Ryu talked about "discussing the matter further" after reports of them going their separate ways emerged in November. She offered an apology for what she said was an emotional response, vowing to be more prudent in her actions and words.

While Hyeri did not specify exactly when her relationship with Ryu ended, she added that she did not actually meet with Ryu again after November. By the admissions of both parties, it does not appear that Ryu's relationships with the two women overlapped, although many in the South Korean public still believe he should have taken more time before moving on out of respect for his long-term romantic partner.

Why people get offended by 'transfer relationships'

Surveys indicate that most South Koreans believe people should take some personal time between romantic relationships -- though the terms of that time and how long it should extend remain elusive.

Matchmaking company Duo conducted a survey on 197 men and 215 women, in which 76 percent of respondents agreed that there does "need to be a gap between romantic relationships."

Of the respondents, 40.3 percent said "people need time to process their feelings about previous relationship," and 22.8 percent cited "there are manners (for the other person) when breaking up." When one's former romantic partner immediately started dating another person, 52.9 percent said they suspected hwanseung yeonae.

An October survey by matchmaking company Gayeon with 217 men and 111 women showed that 57.1 percent of respondents thought "I've fallen for another person" was the worst comment possible in a breakup. It also showed that 35.1 percent thought the other person "transferring" to a new relationship was the most baffling situation when breaking up.

Being accused of hwanseung yeonae can be detrimental to one's social life as well.

A 27-year-old woman surnamed Kang said she once became embroiled in such a complicated relationship while attending university in the US. Her boyfriend had been involved in an on-again, off-again relationship with his previous partner, who had thought they were only on a temporary break.

The boyfriend, who thought they were broken up for good, went on to date Kang. The incident led to her friends pointing fingers and casting her out of the social group, accusing her of impropriety.

As in the case of Kang, many incidents of hwanseung yeonae occur when two people are not on the same page in their relationship.

Han Won-jeong, a manager for Gayeon, explained that much of the friction in a breakup derives from two people having different feelings toward each other. "When the two people's stance (toward the relationship) is not the same, breaking up can be more difficult. A breakup involving a third party can be more shocking, but it could also lead to him or her letting go more quickly," Han said.

For many people, the reason they take issue with hwanseung yeonae is that they suspect the foundation for the new relationship had been laid in the ruins of the previous relationship, even if the person did not cheat outright. This, they believe, shows a lack of respect for a person they once claimed to care for.

“When my boyfriend starts dating immediately after we’ve broken up, I have to wonder if that relationship hadn’t already been started,” said 32-year-old Kim Hee-won, who experienced what she suspected was a “transfer” on her ex-boyfriend’s part. “When you end a relationship, particularly one that has continued for years, I think it takes some time to recover. Not needing such recovery time leads me to suspect that the relationship wasn’t so devoted after all.”