Suddenly Seventeen (2016)

Both of these movies show how the main lead grow and relearn how to make themselves happy.

28-year old Liang Xia and 34 year-old Mao Liang have been together for 10 years, and living together for 5 years. Liang Xia assumes that Mao is going to propose after 10 years of being together, and had given up her dreams on becoming a painter just to stay with Mao. However, she is disappointed when the diamond he had bought was for his boss, Mr. Gao's wife to earn her support in improving his design company. Her friend suggests to Liang that she should force Mao to marry her by proposing to him in public. However, the plan backfires and Mao ends up breaking up with her. The devastated Liang eats a magical chocolate, transporting her memory back to her 17-year old self. Without the worries of adulthood, she is back to her naive, optimistic self and that triggers a surge of interest in Mao, who she now refers to as “Uncle”. Things turn even more complicated when Liang Xia's 17-year old self falls in love with another man, Yan Yan.

Both movies involve time traveling, but in Akko's Secret, the elementary schooler becomes her future self and.... wait for the surprise in the end! :D

The character travel back and forth from young to old and old to young.
Somewhat comedy
Fun watch. Not too serious. Good acting.

Hyun Jae is only 19-years-old, but he has a terminal illness and he does not have much time left to live. He leaves the hospital and goes back to high school. There, he falls in love with Soo Min.

The girl MCs after experiencing hardships during their relationships in life had a total personality change. Through a series of events, they became seventeen again solely in mind. If you don't believe this was properly explained, you can read the summary. Love @ seventeen is a series whereas suddenly seventeen is a movie. They are both very similar but I cant explain without spoilers. Enjoy!

Both FL have a breakup after being in a long term relationship and travel back to their past to their high school selves and falls for someone else

Both female leads were adult in the thirtieth but mentally as a teenager.
Somewhat comedy, fun and easy watch.
Quite romantic.
Cute couples

The unhappy adult main lead (s) travel back to youth period, where she and they were happy, careless, energetic and having fun. It is an easy watch romantic comedy

Both main leads are women who learn to discover who they used to be in their youth and how to live life to the fullest. A great pick me up (the both of them).

Very happy, youthful rom-coms

Both have verses of herself younger......................................................................................................................

A young boy from a working-class family and a bored young girl from a rich family are falling in love. Soon, she's pregnant and the teenagers have to escape from their disapproving parents.

Matsumura Ryouko is a popular novelist in her 50s who has just found out that she has Alzheimer’s disease. In order to gain some fulfilment in her life, she decides to be a guest lecturer at a university. Through one of her students, she meets a South Korean exchange student, So Chan Hae. As they become closer, they fall in love.

Both female lead travel back in time.
They have a lover in current time and an admirer in the past time.
Funny comedy
There is a water scene where the female lead floating in there on both

Thw beginning starts off the same in both movie and drama... couple in a 10-year relationship, girl expects a proposal but the guy is a workaholic and doesn't really want to get married. Time-travelly magic then happens which is where the drama and movie start differing from each other. Both have very good storylines.