My Fated Boy

In both dramas the leads' parents were best friends so the leads grew up together before the ML went abroad to study. The ML returns and reconnects with the FL at the beginning of the drama, and moves in with her shortly after. In both dramas the FL is a bit worn out by her work and previous disappointing relationships. And in both dramas the ML is bright, energetic and brings a spark of joy back into the FL's life.

Noona romance. In My Fated Boy, the FL is a hard working executive secretary who puts more energy into her work than she puts into looking after herself / her apartment. In IHYV, the FL is a public defender. Although she doesn't put maximum effort into her work because she is jaded and expects the worst from people, her job is still demanding and she doesn't take great care of herself / her home is messy.

In MFB, the ML and FL grew up together and the FL protected the ML when he was bullied. The ML developed a crush on the FL and wanted to grow up to protect her, and held on to those feelings steadfastly as he was growing up. In IHYV, the FL helped the ML after a tragic event when she was a kid and he was a little kid. The ML fell for her then and vowed to protect her. The ML in IHYV also holds on to his feelings steadfastly.

Both dramas begin with the ML meeting the FL again after a long time apart, and moving in with the FL shortly afterwards partly to protect the FL but also because of their hidden feelings for the FL. Both MLs are young, energetic, clean (the type to comment on and tidy up a messy apartment), reliable and affectionate.

The storylines are quite different, but the shows have a very similar vibe and feel to them. And in both, the female is a strong career woman, the male leads do the cleaning and cooking while also being successful in their own careers. The relationship between the couple is a bit similar, with the male leads being supportive even at their own expense.

If you are a dramaholic & have seen a few dramas.... when you watch a drama another one that you have watched pops into your head. As I was watching "Hello Again!", "My Fated Boy" came to mind. Both.....
-ML met FL as youngsters
-FL & ML are separated for some time before meeting back up
-ML aggressively & adorably pursues FL
-ML never loved anyone but FL
-FL w/ issues is helped by ML

The FLs in both dramas are older than the MLs.
The women value their careers and work hard to achieve their goals. The male characters both have a role to play in the professional success of the FLs.
The MLs start out in the professional world and want to succeed in their dream as a Designer in The Rational Life and as a musician in My Fated Boy.

Same male lead
Similar in a way that male lead and female lead were like brother and sister with female lead being elder. Then the male lead has feelings for female lead from a very long time

Both are about childhood friends who reunite. Both MLs fall long before the FL, and chase her. Both MLs become strive to become famous (actor vs. singer) for the sake of the FL.

Older professional, competent female lead with talented (music in My Fated Boy, Badminton/Tennis in Nothing But You) younger male lead.

Both are romances with an age gap between the main couple (younger ML and older FL).
...............................................................

Older woman/ younger man romance
Woman is career oriented
Supportive male lead
working relationship, both in the same work environment

Both are heartwarming stories. And you will definitely love the childhood part in both of these shows

-this also a older woman younger man story.
-the ml also try to succeed to return to his love.
-also the woman is his first love.

The main couple are childhood friends/playmates who now have a distance between them (due to their age gap vs. one's popularity), despite the ML's crush on the FL which the FL is unaware of. Both MLs are very popular while the FLs are not. Each episode opens with a cute clip of the two as children getting into mischief.

Both MLs are younger than the FL, with the two childhood friends and neighbors who have now reunited as adults. The MLs have a long time crush on the FL who work in an office. Both dramas have cute tags at the beginning or end of flashbacks to their childhood.

FL and ML have the same age gap in both dramas, with the younger ML falling first, but the FL viewing him as a younger brother for years before finally accepting him.