[Edited 8/29 below]

Kim Joon Ha is the ONLY main character that is unrelated – as far as we know – to any of the 3 major families:  Gong, Oh and Jang.

No family, no childhood history, no backstory. I started to explore several weeks ago. Putting it here so it can be edited as new information becomes available.

tvN Character description of Kim Joon Ha: “Oh Yeon-doo's ex-boyfriend and investment expert. Yeon-doo's baby's biological father. An investment expert. He became an influencer by appearing as a mentor in various media due to the stock investment craze. For him, who thought it was an investment at the time of marriage, Yeon-doo was a stable investment destination. However, he changes his mind when he meets a woman who makes him want to risk it all.”

From Actor Jung Eui Jae and other web sources (interviews and articles)

Joon Ha’s family “is not known yet . . .  it’s a secret.  If you watch to the end, you will know.” 

“When I first met the director, I heard a more detailed explanation about Joon Ha and various points that I was curious about.” 

On how similar he is to his character in the drama, Jung Eui Jae said, "I think we're alike in that he values his job a lot and does his best. I also work really hard to think hard about my own acting because I want to be a professional at my job."

Jung Eui Jae gave his own interpretation of why love is so important to his character. "Kim Joon Ha shows [his] innate character the most in the face of love, and I think it's because [he's] hungry for love [“affection”]. [My emphasis]"

His biggest Achilles heel (aka “deficiency”) is “related to love”.

“He has a persistence and tenacity.  The downside is that [he’s] a little overflowing with that tenacity, so . . [he] gets caught up in various incidents.”

Jung Eui Jae “thinks” that Joon-ha’s goal is to “have a happy family”

Joon Ha is a “self-made” man.  He is “very smart”

From the drama TRHC:

His mother is dead (“I swear on my dead mother’s grave”)

He is MENSA level smart

He owns three homes – two in Seoul and one in NYC [the message to Koreans is:  this man is VERY wealthy]

He gave a seminar for unwed mothers on achieving financial independence.

EDITED ON 7/20/23 - I MADE A BIG MISTAKE!

His birthdate is:  July 01, 1990 (not July 01 1991 as previously written)

8/29/23 edit:

When Joon-ha was 16 years old, his parents died in a car crash in the United States.

When JH was in college in the United States, his older sister (6 years older) became a nun. Her name is Eka.  

Joon-ha's mother name is Shin Myeong Hee.  She is the daughter of Grandmother Gong; she was handed over to an orphanage at a very young age.  As an adult, she provided a DNA sample to the "missing persons" DNA data base.  It was a match with Grandmother Gong.

Although Eka is a direct descendant of Grandmother Gong (proved via DNA test), Joon-ha is not.  As of Episode 46, he does not know who his bio parents are although, assuming his adoption was legal, he is legally a member of the Gong family.  

I think TK and JH have the same father and different mothers. I think their fatherwas a playboy. He both impregnated both mother witout marrying both. JH and TK were so invested in helping unwed mothers probably projecting their inner frustration of how their mothers both suffered because they are both unwed mothers.  TK and JH are both smart, have the same taste in women, cars, hotels and other things.  

I am inclined to agree with you, as you have probably noted in my previous post. It is interesting that the twin sequence happened when they were both at the unwed mother event which would support your theory. I was thinking somehow they were fraternal twins but I couldn't quite figure that out. It would make more sense that they have different mothers. Perhaps the twin sequence was a way of hinting at them having the same father . By the way do you know if there's a quick way to navigate to the Post I receive notification about when someone responds to my posts

Maybe the grandmother knows methin of this and that is why she is so hard on TK about his supposed womanizing. From what I can tell he has serial relationships but just does not want to make any of them permanent.

I dont think they were fraternal twins by the things we know from previous episodes. They have different mothers, JH mother died( unless JH was given away by IO and was adopted by her mother.because  IO cannot afford to support both. But she was a teacher so not exactly very poor so that she cannot afford to bring up both. If  JH is a twin of TK then TK's mother IO is even more evil than she is actually now. How come you can threw away a son and bring up another son  and  not felt gulity?  She even played mother to his husband's children. 

But from information from other posts, I think TK is older by a month born in the same year. ( I cannot find the post) so they cannot be fraternal twins.  I am not  exactly discounting this twins theory ( he had  a twin gene because YD had a twin pregnancy, or YD had a twin gene if we consider Jay and DW). It might be that JH is registered late by a month because that is when he was adopted or left behind in a baby box.   (https://english.hani.co.kr/arti/english_edition/e_national/613412.html

Why can we explained the " hungry for love" narrative. If JH was adopted by his mother, he was not a blood relative and probably neglected ?  ( the same  reason TK was lonely, distant and cold).. Or JH.s mother is so devastated by the betrayal of JH.s father that he neglected his son ( the cause of her "suffering"). 

Another similarities of both JH and TK, they are both womanizer( TK had a lot of girlfriends in the past) while JH is a two-timing jerk. 

as for this question: By the way do you know if there's a quick way to navigate to the Post I receive notification about when someone responds to my posts

You should have log-in and it will show  your MDL page .  Go the bell sign on the left side of your MDL  page  ( near your name ) and click on that bell and it  will give your notifications. Click on your notification and it will bring your notification page. This notfication page gives all notifcations ( present and past comments on all the shows you commented on). The drama that you commented on have blue ( not black) letters, Click on these blue letters and it will give your comments and thhose who responded to your commenst. I hope this will help you. ( I am sorry if it is not clear but if you have difficulty, then just ask . I will try to help)

 shinhwafan:

Maybe the grandmother knows methin of this and that is why she is so hard on TK about his supposed womanizing. From what I can tell he has serial relationships but just does not want to make any of them permanent.

Probably grandmother is aware that  TK's father was a womanizer and so does not want TK to go to the same path and impregante women without taking responsibility. 

In the  same regard, JH impregnate YD without taking responsibility for it. So JH was following the path of his father (if my theory is correct regarding JH's and probably TK's father as a playboy).  So the irony of it,  JH  suffered because of his mother as unwed single mother but he had done the same thing to YD ( although he want to take responsibility now after telling YD to have an abortion ). This is probably what the  actor ( Kim Eui Jae) was alluding to that we can sympathasize with him if we follow the show to the end. 

At this point it seems like the only father's stepping up for his child or maybe not his child is TK

I could imagine a Redemption Arc for the cheating ex-boyfriend. It would be that he realizes his motivation is egotistic and not to benefit yd or her child and he backs off. It would be more fun for me though if he is not the bio dad and ends up with egg on his face

 shinhwafan:

"But from information from other posts, I think TK is older by a month born in the same year. ( I cannot find the post) so they cannot be fraternal twins.  I am not  exactly discounting this twins theory ( he had  a twin gene because YD had a twin pregnancy, or YD had a twin gene if we consider Jay and DW). It might be that JH is registered late by a month because that is when he was adopted or left behind in a baby box."

Over a month ago, I posted on various forums that I had zero doubt that they were fraternal twins.  Not only the cars, clothes, etc but also the way they took an instant dislike to each other (in the elevator) before they knew who the other was.  Also, the way they fought - rolling around on the ground like children, not grown men.  These were all NON-verbal cues.  

I also believe it is too much coincidence that the birthdates are LESS THAN 30 DAYS APART. In Korea, you must register a birth w/in 30 days of birth and you must submit a certificate of birth signed by hospital/doctor/or midwife.  So, I was very willing to believe InOk gave birth to twins but was told that one of them died shortly after birth (so a certificate of birth would exist) and the baby was actually abducted from the hospital.  It's a classic soap opera trope in the United States.  This would also explain InOk's passionate devotion to her son.

However, once the Strawberry arc began, Joon Ha's story - such as we know it - fits better overall with her.  It would make him a Gong family member and  half-sibling with TK.  

I'm glad you have read my post and it sparked a conversation (it's over a week old) because I spent a lot of time translating videos and articles to find some of the information.  :-)

Are you thinking JH is strawberry sun? I am thinking that yd's mother is strawberry.

 shinhwafan:

Are you thinking JH is strawberry sun? I am thinking that yd's mother is strawberry.

The reason I question Bong Nim (YD's mother) as Strawberry is that her brother (YD's uncle) TWICE said:  you inherited your excellent eyesight (or similar words) from our father.  Does that mean it's 100% true?  No, the writers could be planning that (1) the Kang family adopted strawberry several years before Uncle was born and he (and SHE) just assumes that her good eyesight is inherited.  In-country adoption w/in Korea was almost unheard of 60+ years ago so this is still unlikely. (2) somehow the grandmother's mother-in-law (that took strawberry) knew the Kang family and although there was never a legal adoption they raised her as one of their own.  Possible?  but unlikely that another poor family would add another mouth (baby/toddler) to feed as a family member.  The standard practice 60 years ago was to leave a baby with an orphanage, but if the baby was toddler age (2-3), it was unlikely to be adopted

But anything is possible.  

I wanted the fraternal twin story.  I don't want Joon Ha to be a "Gong" - I wanted him to be InOk's son.  But, that now seems unlikely.  And, it certainly brings Joon-ha full circle into one of the three main families because the idea of  incest would not be tolerated in Korea (or anywhere, for that matter), so that immediately eliminates Se Jin and YD bloodlines/families.  

 Kathryn_51:
So, I was very willing to believe InOk gave birth to twins but was told that one of them died shortly after birth (so a certificate of birth would exist) and the baby was actually abducted from the hospital.  It's a classic soap opera trope in the United States.  This would also explain InOk's passionate devotion to her son.

I have not thought of this trope when I was thinking of possible scenario if IO gave birth to twins. It might explain that IO  is not aware that the second twin (JH) is still alive. But who abducted the twin " the father"? or the reatives of the father? 

If not, JH is the son of Strawberry?Then he is a member of the Gong family?   then TK is step-cousin of JH. There is no blood relation between TK , JH and YD. But it is messier scenario where JH can exert more influence as a jerk. He has more more power (due to the guilt by grandmother who will be biased to JH). It will not explain the same taste in everything between TK and JH

IF BN is Strawberry, then TK and  YD are step-cousin (still no blood relation). I do not think it is incestous. Incest is defined as sexual relationship with blood relations ( https://www.britannica.com/topic/incest). Ha Neul is still legitimate Gong granddaughter and will be treated  favourably. 

 if jH and TK are fraternal twins with abduction trope or TK and JH are brothers by the same father but different mothers, it will at least foster some mending of the relationship of TK and JH. As they say, blood is thicker than water. It will also explain similar taste trope. 

 Kathryn_51:
The reason I question Bong Nim (YD's mother) as Strawberry is that her brother (YD's uncle) TWICE said:  you inherited your excellent eyesight (or similar words) from our father.  Does that mean it's 100% true?  No, the writers could be planning that (1) the Kang family adopted strawberry several years before Uncle was born and he (and SHE) just assumes that her good eyesight is inherited.

I do not understand why you brought this up, good eyesight. are you alluding to Grandmother's (Gong) eyesight ( which is contrast to BN's good eyesight? Chung Mung (eldest son) said that Grand ma has poor eyesight  but refused eyeglasses for a long time.  So grandma always ask his grandchildren to call for people on her phone citing the excuse that grandma's eyesight is poor. I do not think that her eyesight was poor in the past ( she uses glasses now because she is 80 old) but when she was younger, the reason why she asks her grandchildren to call people is because she is illiterate, She cant read. She hides her iliiteracy by asking people to do things for her like reading , using the phone.

I noted in another post that Dong Wooks daughter was wearing strawberry pajamas in a scene.. At another point I think it was BN was wearing something that was all stippled red dots. Are these hints?

 joji_d:
 if jH and TK are fraternal twins with abduction trope or TK and JH are brothers by the same father but different mothers

Is there a problem with brothers (TK and JH)  having sexual relationship or marrying the same woman in South Korea. Is this considered taboo? I think this was tackled with 2003  drama series https://mydramalist.com/2758-snowman starring Gong Hyo-jin, a girl who falls in love with his older brother in law. 

according to Wikipedia (https://en.wikipedia.org/wiki/Article_809_of_the_Korean_Civil_Code)

 Marriage may not be allowed between parties whose relationship of blood relative existed within the sixth degree of adoptive parents lineage and within the fourth degree of adoptive parents affinity

 so if BN is Strawberry, then YD and TK cannot marry, which are insurmountable obstacles to our main OTP.

I think , probably Hee is the daughter of Strawberry.  But how old is Hee ( is he as old as Uncle Daesang) then he is only a few years younger than BN ( who is 59 years old).  i I have discussed this theory if JH is Strwberry's son  in above post. 

The writers have a big job to be out of this mess. They might introduce another character?