In both shows:

1. Yoo In Na plays the female lead.
2. The female lead is an actress who has lost popularity.
3. Female lead is a bit of an airhead, but persistent.
4. The characters learn from each other.

In both shows...:
-We have two stories being told at the same time. One deals with the present, the other with their past lives.
-Two of the three main leads have been reincarnated, with the third lead having waited a long, long time to reunite with them.
-They both have a fantasy aspect to them.
-There's a love triangle in present throughout most of the show.
-There's a second female lead pining for one of the male characters.
-FL has memories of something that happened in her past life but she's unsure which of the two male leads does it relate to (slight mystery aspect).
-There's sweetness, comedy and a bit of tragedy to both.

Both shows:
1. Are parodies of their genre, as such the comedy takes precedence over everything else.
2. Despite the absurdity, there's a good and heartfelt plot at its core.
3. There's a lot of character growth from the main leads.
4. Main leads establish a balanced relationship, in which they bot learn and get something from each other (rather than one having all the power).
5. FLs kick as in their own way. They don't allow anything to stop them, always take the initiative and are pretty active.
6. MLs are soft guys with a tough exterior and they trust and rely on the FL.
8. FLs have a support group of friends.
9. Antagonists/villains are over the top and slightly on the cartoony side (which adds to the hilarity).
10. There's a love triangle in both series, with a SML pinning for the FL.

In both shows...:
1. There's a fantasy aspect to both shows and the visual effects are a bit silly in both. Magic is used in both shows.
2. Both shows are very lighthearted. A feel-good drama that doesn't ask much of its audience.
3. In MF&TW, the FL is a fairy, in WL she's a witch. Both rely on other people's belief/acceptance/love in order to stay healthy.
4. There's a love triangle that makes you unsure who the FL's "fated love" is supposed to be.
5. ML is socially awkward and inexperienced in love. He's also a bit cold to the FL and doesn't try to understand her at first.
6. 2ML is sweet, believes the FL and is always ready to lend her support. MF&TW's ML is much more adorable, though.

In both shows:
1. FL is played by the same actress.
2. FL is very opinionated and stubborn.
3. ML doesn't know how to play politics and, as a result, they end up with a lot of enemies and no friends.
4. ML's are very capable at their jobs, though their underlings don't really feel connected to them.
5. The relationship between the leads is quite rocky at the beginning, with the ML's unable/unwilling to trust them.
6. The antagonists are quite cartoony. One of them is even played by the same actor, who has a similar role in both shows.
7. There's a lot of absurdity in both shows (the comedy is more like a parody).
8. ML is the FL's boss.

In both shows:
1. The female lead caused the ML to incur psychological/mental damage. In the case of HMKM, his personality splits. In the case of DJ, the ML becomes unable to distinguish faces.
2. ML is forced to keep his mental issue a secret, forcing himself into isolation.
3. ML's secretary is the only one in the know about the ML's problem and they work extra hard to try and find a solution.
4. The FL becomes a special present for the ML, who helps them deal with their problem. In a way, the FL becomes something of a "safe harbor" for the ML.
5. FL is loud, open and able to speak their mind.
6. Unlike the ML, the FLs are very close with their respective families.

In both shows:
1. ML suffers from a mental problem. In the case of TBI, ML can't recognize faces. While in DJ the ML has lost his ability to form short-term memories, causing him to forget the previous day.
2. In his attempt to protect the FL, the ML gets run over, which causes his disability.
3. ML is the heir of a big company with plenty of enemies trying to take them down. As a result, they are forced to hide their disability from co-workers and family alike.
4. The ML's secretary is the only one who knows about his disability.
5. FL are both actresses. Though DJ's FL has lost her popularity by the second episode.
6. FL's are hard workers and have a tight-knit group of supporters.
7. ML becomes super sweet once he falls in love with the FL.

CONTAINS SPOILERS*******************************************************************************************

In both shows:
1. Female lead caused the ML to incur psychological/mental damage. In the case of HMKM, the ML's personality splits. In the case of TBI, the ML becomes unable to distinguish faces.
2. ML is forced to keep his mental issue a secret, forcing himself into isolation.
3. ML's secretary is the only one in the know about the ML's problem.
4. The FL becomes someone who helps heal the ML.
5. FL is loud, open and able to speak their mind.
6. The leads start their relationship with a binding contract.

In both shows:
1. Female lead os attempting to find out her identity. In LMIH, FL lost her memories and she's trying to get them back. In Mask, FL must study the life of the girl whose life she took over in order to survive.
2. Female leads are active protagonists of the story, meaning they are always taking action.
3. Female leads are in a difficult position, with the antagonists targeting them.
4. Male leads are both protective over the female lead, but they aren't forceful and allow them to make their own decisions. They also have issues with one of their parents.
5. Female lead lives in the lion's den. Meaning, she's constantly surrounded by antagonists and danger.
6. Both shows are heavy on intrigue, so they can be a bit slow paced.
7. Events are explored and understood through the use of flashbacks.

In both shows...

1) Female lead missed out on her youth (though for very different reasons).
2) Female lead tries to figure out her place in the world and, as such, go through an identity crisis.
3) A situation forced the female lead to give up on her dream. For Twenty Again it was dancing, for Thirty but Seventeen it's playing the violin.
4) Female lead still have a "high schooler" personality, though it's more natural in Thirty But Seventeen than in Twenty again.
5) Female lead met the Male lead when they were young (highschool).
6) Female lead was Male lead's first love.
7) Male leads are both emotionally stunted.
8) Both series are lighthearted but so far Thirty but Seventeen's story is superior.

1) Female leads are both a bit unconventional, fun and very lovable. They aren't afraid to voice their thoughts.
2) Leads' relationship starts on the wrong foot, but they become friendly soon after.
3) Second male lead in both are very gentle and caring towards the FL. They come into the FL's life almost like a knight in shining armor.
4) MLs' are a bit arrogant but also very good at their craft. They do have an adorably childish side that makes it fun to watch them.
5) There's a love triangle in both, but it's more drawn out in The Greatest Love, with the FL being more indicisive.

1) Not only is the FL played by the same actress, but the characters are very similar in personality. They are both hardworking FL trying to navigate their difficult careers.
2) MLs are also similar in personality (arrogant and dramatic). In both series they work in the same place as the FL but are ranked much higher. They sort of end up taking FL under their wing.
3) 2MLs don't work at the same place as the two leads, but they are very gentle and caring towards the FL.
4) Love triangle also takes place throughtout a big part of the series.
5) Overall it's a similar feel, but The Greatest Love has more interesting characters.