End Game Theory

This might seem too far-fetched but it is still a possibility. I am pretty convinced with the theory that Heedo's mother has a dementia and this would be a big part of the plot twist later on. I've thought about it as I remembered an article I've read when casting for this drama is still not confirmed. It said that Yijin's character will go through several undercovers like being a make-up salesman to report about something (I don't really know if they somehow changed this or something). If this would be the case Yijin's career later on would likely be an investigative reporter hence, he could be the dad that they were referring to who can't go back because of quarantine rules. He may have changed his name not because of the debts that their family has but because he might have encountered a case that would endanger his life and the life of his family. If this would be the case, this might explain why Minchae did not recognize baek yijin at first as they could have eliminated a lot of proof of existence of Baek Yijin. The news that  IMF crisis in Korea I believe lasted for only a few years and if the information i have found is correct, the crisis ended around 2001 and 2002. So there might be new progress with regards to yijin's father's case. So, my best guess would be that if the name was really changed, it would be because of his work and not his father's debts. Another theory connected to the new identity of yijin and the mother having dementia is that the relationship between the mother and heedo was never good until several years later maybe until the time minchae was born and that heedo's mother was always against yijin. The pictures of baek yijin and na heedo as well as the diary was still there as heedo might have left it there when she became married because of their (mother and heedo) sour relationship.

I believe this is how they will go about the ending:

1. Yi-Jin and Hee-Do are very much together, but not in the 'conventional' sense. They aren't married, but are co-parenting Min-Chae. Because first half of their life, Hee-Do was busy touring internationally as an athlete, and later, Yi-Jin is touring as an established reporter.

2. Since they aren't married, they decided Min-Chae would not have either of their last names. Kim is Yi-Jin's mom's last name, so that works? [I also noticed how Yi-Jin's maternal uncle is a bachelor, and their blood-line ended with him & Yi-Jin's mom. I wouldn't be surprised if Yi-Jin's Mom tearfully asked him to consider 'Kim' as the last name for his children, esp since he's not 'officially' married. I also think Yi-Jin would 100% humor his Mom, and Hee-Do is too chill to ever care for her kid's last name]

3. Yi-Jin & Hee-Do would have exchanged rings for sure, but never registered officially. This directly calls back to how Hee-Do believes her Mom must have sold off her wedding ring, and Yi-Jin's parents being in love, but 'divorced on paper'.

4. In fact, going by the year, Hee-Do would have been pregnant with Min-Chae in 2005 (as she is 15 in 2021?). Hee-Do would be 25. Now because they actually fell in love at 21 & 25 respectively, I do believe Min-Chae is a younger sibling. She has an older brother (with the same last name Kim) who's 18 at this point, who used to live with Yi-Jin. [The 'separated siblings with unconventional last-names' trope from Start-Up, yes!]. We'll see a family re-union right in the finale, when Yi-Jin comes back home along with Min-Chae's older brother! [this also lines up with the fact that it's probably December 2021 in the show, and also Christmas vacations!!]

5. Because Hee-Do's life unwillingly mirrors her mom's (i.e. unintentionally being a single-mother), I believe Yi-Jin's also has to mirror his parents (i.e. being a separated couple because of circumstances, 'older sibling with dad, younger sibling with mom' kind of an arrangement) for the sake of creative & poetic continuity!

6. Tvn loves doing these dramas, where families and couples don't have an unconditional 'happily-ever-after' together. Yet, the times they are together... are some of the moments when all of them truly come alive! I think Crash Landing on You is one such example! ^^

7. I believe Min-Chae's package from Dad was an international package, no wonder he has no idea 'what's in trend' these days! xD

Edit: I posted this hidden under the spoilers tab. It might get lost... so I posted this here! :D

With each episode, I'm feeling more confident about my theory. BYJ and NHD are married. They adopted the kid. YR is dead. She was a very crucial part of HD's life so that would explain why she doesn't want to talk about those memories and why she seems a bit dull in the future. It's because her love for YR is just as strong, if not stronger, than her love for YJ at the moment. Also - still feel that JW and SW end up together. There's a time jump so they can actually afford to dangle other ships until then. While the ship is adorable, they've used every opportunity to reiterate how JW is only pursuing YR because she is pretty and that doesn't seem like something that'll last that long. That would also explain why the kid doesn't seem to recognise the others also. Maybe they all grew apart after school and after YR-JW break up. TBH when it comes to JW and SW, they seem close to the others but it's obvious that at the end of the day the only person each can't live without is the other. 

The thing is, drama has been hinting about SW liking JW for sure for a long time, and it sealed the deal in ep 10.

ep 10 - When JW confessed to YR, SW heard it.. and dropped everything.. we didn't see her reaction.. and when the other two noticed her, she pretended to be fine.. but really too much of a coincidence to be there and dropping everything as if she were shocked

Every little interaction between the two of them and the preview of in the class room.. this is childhood love trope 100%

Most importantly, what is the purpose of SW in this drama? 

And, i really don't like that YR's dad drives a truck.. and a white truck at that.. in kdramaland that is literal definition of doom

I enjoyed all the episodes but kinda get anxious at the end of every episode bcs they always tease us that there will be plot twist at the end of the story. 

The theory that I always think of:

1) Probably Heedo and Yijin will end their relationship at 2521 (I dont want this actually ㅠㅠ ㅠ)

2) Yijin change his surname bcs probably they will have athlete-reporter scandal. Do you guys notice that there are scene where it shows the camera that shoot their trip at the beach? Maybe there is nothing but I kinda sus that there will be something happen in next eps. But kinda have loopholes where Minchae didn't recognize Yijin's face. 

3) Kinda agree with DramaReign in post above that probably Minchae mom is Yurim. I think that in the present scene that there are no signs / people call Minchae's mom as Na HeeDo (Please correct me bcs i didnt remember all the previous scenes >.<)

At the end of ep 10 where Minchae's mom said that "nothing last forever", I thought there will be end of Na Heedo and Yijin relationship BUT probably there will be change of the story where the five friends will have some plot twist. 

Enjoyed all the theories above and I feel that we can be a writer ㅋㅋㅋ ㅋㅋ

Really hope that we can get happy ending for all of them 'finger crossed'. 

Guys, Yijin is adopted.

You may read this theory: https://twitter.com/dewrainyeonu/status/1503240139551965184

my theory is that baek yijin and hee do won't end up together and I think the dad is someone else who haven't been shown yet 

 thematchabun:

Putting this theory here so I can come back to see if it stands correct although i don’t want it too. 

https://mydramalist.com/695149-twenty-five-twenty-one#comment-9043643

please prove me wrong writer ????surprise me. 

I love how perfectly your theory makes sense but i hope you're wrong haha. But in case you're right, what if "25-21" is not a reference to YJ and HD? Maybe it is a reference to YJ and YR because that's the age at which they both died? We know that the older-age scenes will not start at least until episode 12 so i don't think they have enough time to show much of their relationship and i don't think the ages when they started their relationship will be the most significant for HD to name something over it (If anything, their current ages might matter more to her because that's obviously when she bonded with both the people who matter the most to her while also somewhat reaching her dream). YR must be 21 when YJ is 25 so it'll sort of make sense for her to name her studio 25-21 as an ode to them I guess?