This is similar to an earlier post in mid-November and I decided to re-post/update it here  in the discussion forum.

Why does the character of Park Ga-on exist?  She's not connected to any of the two main families, nor is she a potential romantic interest like Mi-rim. 

In episode 16 [air date: November 18], there is a scene where Tae Min brings a very drunk Hyo Shim home and asks Park Woo Joo for assistance. [puzzling question;  how does TM know Park personally, know that he lives in HS building and also had his phone #??.  We may never know the answer.]  For absolutely no rational reason, Ga-on goes with her father to help and is immediately enchanted with the handsome Tae Min.  He, in turn, was very charming to her. it was a lovely snippet in time.

My immediate thought – 🚨🚨🚨there is some connection between Ga-on and Tae Min. 

Time to research! I posted the following right after Episode 16:

Park Woo Joo:  According to the KBS character chart, Park Woo joo is Ga-on’s "step-father”.  Namu Wiki states Woo-joo is not actually related by blood to his young elementary school daughter, Gaon. “Later, the mystery of birth will unfold.”

“Hannah Young":   She is not on the KBS character chart.  According to Namu Wiki, the character of Hannah Young is Ga-on’s bio mother.  ““She used to be the most successful woman in Tenpro*, but now she is in decline (?), and while working in a provincial town, she sees Ga-on on television and comes to her.”  

Note:  at the time of my original post, Ga-on’s pending appearance on TV was NOT known and the first occurence was in Ep. 22.  So, it indicates that Namu Wiki contributors have accurate insight and unless the writer has re-written the scripts, it appears that the character of Hannah Young will appear soon.

My wild and crazy theory is that that Ga-on is Tae-min’s biological daughter.  That scene was totally unnecessary but her moment with TM was very sweet.  Plus she has become very close and beloved by Grandmother Choi who obviously cherishes her.  I actually dislike the idea but there is absolutely no other rational reason for the character of Ga-on to even exist unless she is somehow connected to one of the major characters in the drama.  Would prefer that she was a sibling (i.e., daughter of kang Jin Bum) but one way or another there is some connection to Tae Min – otherwise Ga-on’s late night meet-up with Tae Min would be meaningless.  Worse, it will be another crisis for Tae Min and now that he's married I dread how ugly this will become.  

I also posted my Second Wild and Crazy thought (only a thought, not a theory) that Uee might play Hannah Young since no casting for the role has been announced.  And it might explain TM's instant-love for hyo Shim whigh according to the flashback/script was when they first met and her hair was down.  

* Thanks to poster kalenahenden who informed us that “Ten Pro” are exclusive adult establishments that are infamous in Korea for catering to only the richest in Korean society. “

With Taemin's mother going out of her way to state that she should have let Taemin fool around when he was younger as the reason for why he was opposing her demands for an arranged marriage, it wouldn't surprise me he actually did sneak around behind his parent's back if Gaon is his child.  Also, Taemin does seem to have a desire for forbidden love in pursuit of the dream of a normal life which his mother opposes because she is from nothing and will do anything to keep herself from feeling worthless by making everyone else around her into pawns.

Hmmmmm. . .I've had a slightly different take.  Mom said they didn't allow him to "date" (or discouraged dating?) so visiting a high-class adult club would be standard chaebol experience -  casual, no commitment.  He wouldn't have needed to sneak around in that family and IF - it's pure speculation on my part -  TM did so, I wonder if a male family member introduced him - Grandpa? Dad? Uncle

If Hannah Young does appear, i think it will be pretty soon. I'm actually rather shocked that TM and Su-kyung got married before this twist because divorce isn't usually considered a "happy ending' on a weekender.  Broken engagement? yes.  Divorce?  No.  

You're probably right on his mother not being upset if he visited a Tenpro. Since his father talked about he once loved wife (but clearly doesn't anymore), then it would make sense that his father was visiting Tenpros and might bring him along. It's still possible that Taemin's father is also Gaon's father, which would make them half-siblings and could also explain their cute interaction. 

I did find it very interesting that the grandmother was adamant about annulling Taemin's marriage as soon as possible since that family is even more cutthroat than theirs which is saying something.  He is on parallel journey to Hyoshim about being too subservient to his family and to grow he needs to break free and become independent. He was loyal to his family but will he feel the same burden to be loyal to his wife's family who forced him into this union with threats.  The big question is will this marriage crush him or will it make him rise up like a phoenix from the ashes. 

Though only the leads are guaranteed a happy ending and Taemin is a Second Male Lead. The Second Male Lead and Second Female Lead from another weekender I watched last year did not get a happy ending because the SFL was a villainess (though they did humanize her at times). 

Over the last several episodes, I've noticed some rather significant "revisions" to prior history/facts, especially those involving the accident at Daegwallyeon pass.  it's possible 'Hannah Young" may have been originally planned as a mid-season plot twist, but Step-father Woo Joo doesn't seem too worried about Ga-on performing any longer, so perhaps the writer decided to dump that story.  

Tae Min may not be the "romantic' male lead, but he is one of three 'main' roles and therefor I think he gets a happyish ending but after Ep. 29, it's likely that Su-kyung will not.  She is a mere plot device to make his life miserable.  Which is why I  was shocked by the wedding - it's easy to break an engagement, but divorce isn't easy on a family drama.  I was even more surprised that Grandmother was opposed to it since Su-kyung's father once said they were once close friends.   Maybe annulment is the answer, but i really wanted the two to be together and a redemption arc for Su-kyung just doesn't seem to be in the her future.  At least Tae Min is trying to discover the truth about Daegwallyeon Pass.

Could you tell me which drama involved the SFL didn't get a happy ending?  This is my 2nd weekender and I vowed I would never watch another one after TRHC - but then Ha Jun was cast and that's why I began this.  I wish I had kept my vow - I really don't like it when the writers ignore prior facts and create brand new ones.

Unless writers intend to completely reverse course, Grandmama wants trusts Tae Min and wants him to lead Taesan Group, she doesn't want any public scandal regarding his parents  and she wants Tae Ho to be safe.  But Tae Ho - the most bi-polar character i have ever seen in a kdrama - is consumed with hate and his antics are going to put  Taesan Group right into the cross-hairs of TV Live.  Poor Tae Min!!