Recommendations

Both are historical mini dramas and have leads who work as an assassin.
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Both are historical mini dramas and have leads who work as an assassin and a FL who is a princess.
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Both are historical mini dramas and have leads who work for a shadowy origination as an assassin.
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Both leads meet after 10 Years like in A DATE WITH THE FUTURE , Male lead is a Firefighter and their romance that grow after they meet eachother...

both have similar plot: female lead falls for male lead and it’s first love. Both male leads eventually fall in love with female leads. They both have an innocent/youthful vibe!

there's no age gap in IOTNBO but in both dramas:
- the FL is rich (and has a great wardrobe) + has been sheltered (personalities differ though)
- FL pursues ML first and relentlessly chases after him
- has a ML who has things holding him back from starting a relationship with FL (in TFF its age gap and his responsibility as an adult, in IOTNBO its his responsibilities and her personality).
- both have great chemistry between leads
other than that plot varies wildly, but I think it's a good rec to keep in mind if you run out of directly similar ones.

In both series the ML met the FL when she was young. Having to face the struggles of life alone, both ML find solace in the FL through her words, gestures, company, and personality per sé.
In 25,21, they started as friends. In Hidden Love, they started like big brother-little sister.
In both series, there’s a physical separation until they meet again as adults. Then romance will blossom after some time and realizations.

They both are set in modern times at school and sometimes outside of school.

Gives off youthful and slice of life vibes. Perfect to binge-watch to if you are feeling numb!

Both mini dramas have a palace setting and are about the ML and FL who have very different lives swapping bodies due to some natural phenomena.

Both mini dramas have a palace setting and are about the ML and FL who have very different lives swapping bodies due to some natural phenomena.

Both dramas have a palace setting and are about the ML and FL who have very different lives swapping bodies due to some natural phenomena.

Both dramas have the main characters swapping bodies and experiencing a new perspective on life as a result.

Both dramas have the main characters swapping bodies and experiencing a new perspective on life as a result.

Both dramas have the main characters swapping bodies and experiencing a new perspective on life as a result.

Both dramas have the main characters swapping bodies and experiencing a new perspective on life as a result.