Summer X Summer (2007)

the main females like the male main and slowly change his heart.
Joe Cheng is the main lead for both dramas.
Xia Ya and Danson were in Summer x Summer and ISWAK2.

Both drama has the same men leader Joe Cheng. Female lead are very funny and unlucky but at the end they can get their love.

Both dramas' female lead falls in love with the most popular guy at school (the male lead).
One of the various differences: the male leads' personality (in PK he's more rational).