SEOUL (Reuters) - She shops for fish for her family and is not afraid to go out in public in her slippers without a fancy hairdo, but one thing sets "Happy Mrs Jung-sook" apart from other South Korean housewives.

She is the First Lady of South Korea, the wife of popular new liberal President Moon Jae-in.

Kim Jung-sook's upbeat personality and unprecedented openness have earned her the nickname "Happy Mrs. Jung-sook". In barely a month since Moon's election win, she has already set herself apart from former first ladies who lived quietly in their husbands' shadows.

Kim says she wants to fill any gaps Moon might miss as he tries to communicate with a South Korean public wary of established politicians after a corruption scandal ousted his predecessor, Park Geun-hye.

"I would like to be a neighbourly first lady who's down to earth and friendly," Kim said in written responses to questions from Reuters, her first as first lady.

"First of all, I have asked people not to call me first lady," she said.

So it was no surprise that Kim, 62, was seen queuing to buy fish during campaigning for the snap May election. She also makes honey-preserved ginseng for politicians as gifts.

Political observers see her as a breath of fresh air after Park's ouster in a corruption scandal that rocked South Korea's business and political elite.

"In the past, first ladies were seen sticking to formalities, they were serious and never spoke up," said Ha Jae-keun, a culture critic for South Korean media.

"Kim, in contrast, seems approachable and feels fresh."

Her image as an ordinary "ajumeoni", or middle-aged woman, adds to the lustre of Moon, whose popularity has surged because his "common man" touch is in such contrast to Park's aloof and disconnected style.

Moon's approval rating hit a record 83 percent in the latest poll by Gallup Korea released on Friday. By contrast, the unmarried Park's approval rating had fallen to 44 percent just four weeks after she took office.

Park was famous for never going out in public without her trademark highly coiffed hairdo and makeup, her unapproachable demeanour later earning her the nickname of "ice princess".

"It seems that the public that was wounded by Park's coldness is being comforted by Kim," Ha said.

'FEMALE WARRIOR'

Kim and Moon have been married since 1981, and a video showing her brushing his hand away after a minor row during a visit to a traditional market has been viewed hundreds of thousands of times.

While the first couple might argue just like any other, Kim sees her role as helping to keep her husband well-grounded during his single five-year term.

"Our new house is so large and nice but I'm trying to live as we lived before because I know we'll go back to staying in a small house five years later," said Kim.

"I'm trying to make him laugh, make side dishes he is accustomed to and have kept our bedroom small and cosy so he can feel at home in a completely new place," she said.

Days before moving into the presidential Blue House, Kim was seen with a protester who had camped outside her home, holding her hands and asking "why don't you come in for some ramen?"

Father Paolo Ryu Jong-man of the Hongje-dong Catholic Church, where the presidential couple worshipped, recalls Kim calling her husband "my person".

Invited to the Blue House a few weeks ago to give them a blessing, Ryu said they walked with him and some nuns through the presidential compound.

"I told the first lady about how confidently she walks - like a 'female warrior'," he said. "And she replied: 'Oh is that so? Should I walk more like a lady'?"

Ko Sang-man, a human rights activist and executive producer of a play called "Private's Mother", recalled seeing a woman sitting quietly and crying during a performance of the play, which is about mothers whose sons have died, possibly as a result of bullying, during military service.

The woman arrived at the theatre on a recent Friday night after the lights had gone down and Ko thought at first she might have been part of the president's security team. The public only learned it was in fact Kim after Ko posted about it on Facebook.

"I saw a middle-aged woman who was crying, and wondered whether the presidential security team hires women. I also thought she looked a bit old to be in security service," Ko told Reuters.

(Reporting by Christine Kim and Jane Chung; Additional reporting by Haejin Choi; Editing by Soyoung Kim and Paul Tait)