Both dramas have cute main lead couple, FL and ML have great chemistry. Both dramas feature leads that are hardworking and never give up. Also there's this nostalgic feeling in both dramas, because they're set in past (Youth of May -> 70's and 2125 -> 90's, early 2000's). I get a bit similar cinematographic feel from both of them, too.
I think most people who loved one drama, will love the other.

In sweet 18 the ML is prosecutor, while in P to JK ML is a police officer. Both dramas have an older guy falling for a younger girl, both are cute stories and both have cute couples. I really love both dramas, I think if you like Sweet 18 you will probably like P to JK as well ^_^

Both are about teacher-student romance, and while both of them are very cute, My Rainy Days is a bit more serious movie.

They're similar because both of these stories are about younger girl (high-school student) and older guy (teacher/temporary teacher). Both stories are very cute <3 In My Little Bride they're a married couple.

They're both stories about arranged marriage, but Marrying School Girl is about 2 teenagers getting married and My Little Bride is about a teenage girl marrying an older guy. Anyways, My Little Bride is so cute! It's a must-watch, I think :)

''Kiss me" and "Itazura Na Kiss The Movie" are both based on Japanese manga "Itazura Na Kiss", so they both are similar :)

They're based on the same manga ,,Itazura na kiss", so they both have the same plot, except that ,,Kiss me" is Thai and ,,Itazura na kiss" is Japanese :)

Both of these movies tell you a romance story of a teacher and a student. The main difference is that in My Little Bride they're married, but in Kinkyori Renai they're just dating. Well, both are great movies with amazing cast <3