Okay, my theory is this: Baek Yi Jin is dead. He dies at age 25 in 2001 OR he could die at age 26 in 2002.

My theory is that, though highly unlikely, Yi Jin is sent to the US. Open Tennis finals in September of 2001 and dies in the 9/11 attacks before he gets to leave for Korea. This could happen because the US. Open was held until 9/9 in NYC and he could have been sent to cover the event. He could have stayed a little bit longer and get caught in 9/11 while doing tourism in the towers. 

OR....

He could die in a car accident. The drama, according to what I've heard, was based on the song 25-21 by Jaurim. Sources say her boyfriend died in a car accident when he was 26. So that is why she wrote the song 25-21. 

SO FAR, for me there are only two options: whether he's dead, or he's the husband in present times. It would take something HUGE to happen so that Baek Yi Jin will lose contact with Hee Do for more than 15 years. Even more, she doesn't even mention her name. I don't know what the writers are planning, but I'd rather end this as a heartthrob tragedy and have a nice memory of these two than see any nonsense. They better don't play with us. 

I hope no one would die in this drama… like each episode was filled with laughs and happiness, I cannot seem to see that the writer would be cruel enough or morbid enough to kill any of these cute and awesome characters in the end…

I think Ji Yin and Hee Do will get married when Hee Do finishes her career. And when they will be 21 and 25 they secretly register, only family and friends will know about it. And their daughter Kim Min Chae would be named after her grandmother so that no one would compare her to her famous mom and possibly famous father, just as no one knows that Hee Do is the daughter of a news anchor. When Hee Do's mother said that she had recently met Ji Yin, I immediately realized that maybe he had died and she visited his grave. But maybe it wasn't like that, and Hee Do's mom really did meet Ji Yin before her surgery, who came to visit her on purpose? And the fact that Min Chae does not have the courage to fight and does not want to train for the competition. I think she is under stress because she is afraid for his grandmother who is sick and is probably battling cancer. That's why Hee Do and she spend time at her house.

 Izyda:

I think Ji Yin and Hee Do will get married when Hee Do finishes her career. And when they will be 21 and 25 they secretly register, only family and friends will know about it. And their daughter Kim Min Chae would be named after her grandmother so that no one would compare her to her famous mom and possibly famous father, just as no one knows that Hee Do is the daughter of a news anchor. When Hee Do's mother said that she had recently met Ji Yin, I immediately realized that maybe he had died and she visited his grave. But maybe it wasn't like that, and Hee Do's mom really did meet Ji Yin before her surgery, who came to visit her on purpose? And the fact that Min Chae does not have the courage to fight and does not want to train for the competition. I think she is under stress because she is afraid for his grandmother who is sick and is probably battling cancer. That's why Hee Do and she spend time at her house.

surgery? when was there a surgery.. and NHD and KMC are there because KMC ran away from her home... and we did learn that dad was not in the country and is in quarantine right now.. so whoever grand mom met is not dad

It may not have been an operation, but Hee Do and her mother have had a colonoscopy and such tests are not done without a reason.

 Izyda:

It may not have been an operation, but Hee Do and her mother have had a colonoscopy and such tests are not done without a reason.

apparently that was just part of an annual check up, they made it sound like its something normally done past a certain age. 

 Ivy:

apparently that was just part of an annual check up, they made it sound like its something normally done past a certain age. 

Yeah I agree. Definitely sounded like it was just a checkup. I think they chose to use it as a natural backdrop for a mom-daughter relationship scene

Okay I was actually told to check this thread cuz I asked about this in main comments and I stared watching the just today.

I don't think Ye-jin is alive and IF he is then, he's not Kim Min-chae's dad cuz I get why some would say that he changed his surname to Kim (taking his Mother's Surname which actually is Kim) but why wouldn't Min-chae remember her Dad's face? She could get confused with the names I get that but no way she won't know how her dad looked like when he was young. Unless he isn't her dad or perhaps he died when she wasn't even born and hence her mum remarried her Current Dad i.e. Mr. Kim and Min-chae was never told about her Biological Dad or it could be that Ye-jin isn't the the Dad at the first place and either died or lost contact with Heedo.

 Ivy:

apparently that was just part of an annual check up, they made it sound like its something normally done past a certain age. 

If it was just an annual checkup, why did Hee Do said "mom, don't go anywhere , don't go ... stay with me"?

 Izyda:

If it was just an annual checkup, why did Hee Do said "mom, don't go anywhere , don't go ... stay with me"?

cause we start thinking about things like when our parents get older? 

 Ivy:

cause we start thinking about things like when our parents get older? 

Maybe you're right. But it's kind of weird that He Do used just such words. And why did they have the same test at the same time? Maybe they actually have better health care there?

I’m pretty confident that YJ is still alive and married to HD. How their daughter have a different last name couple can be 1) she’s adopted 2) they changed her last name so she’s not tied up by her parent’s reputations.

Why do I think she’s married to HD? Cause if all it takes was for a fellow fencer to make him jealous, there is no way he would let her be married to someone else. The timeframe of when she possibly was pregnant with their daughter isn’t enough time for them to break up, her find someone else what would have that kind of impact on her, get married, have a baby. Plus in episode 13, she pretty much told him whatever their relationship is, he cannot abandon her, she’s not willing to lose him. His response was that he would try whatever he can with her so for her to prepare herself. Lol, this is basically telling us that they are going to make it work! Plus, it’ll be so weird for the daughter to be reading a love story that isn’t her parents. Also, this isn’t a medodrama to so I doubt they will do that to his character. Plus, why focus so much on their love story only to cast it aside as puppy love later on by having her married someone else? So, yeah, I think YJ is the father. 

I don't really have any theories, but when it comes to  Min Chae not recognizing BYJ on pictures it doesn't have to mean that she doesn't know him in the present. They were taken many years ago and he could've changed so much. Sometimes I don't recognize my family members on old pictures too...

HD doesn't need to be biological mother or married. while dad might be biological dad


maybe MC just calls HD mother

Maybe Min Chae is Ko YuRim's daughter and Heedo adopted her because something happened to YuRim? I just don't want YiJin to be death