Hi My Sweetheart (2009)

Both of the MLs are seeking 'revenge', with the FLs being clueless about who they were until like the last 6-7 episodes.

In both dramas the lead hides their true identities in order to get revenge on someone from the past... but those pesky feelings get in the way!

Both deal with the pure love story between the rich and poor who broke up because of their parents. They meet years later and still have feelings for each other.

The lead (male/female) finds someone that looks exactly like their lost lover, then fall in love all over again.

It remind me of this drama with similar story line of group of adults who got friends opposite sex & they all try overcome obstacles & hardship in their friendship. Starring famous Japanese actor & actresses.

Male leads are naive or apparently “not smart” at the beginning. Female lead has a temporary lapse in judgment and goes for the educated second male. Hurt, both male leads reform themselves and pursue the female lead again with ulterior motives and for revenge.

Hi My Sweetheart and Why Why Love have several common characteristics
-Both feature Rainie Yang as the lead actress with romance stories between several male actors
-Both use simplistic Taiwanese dialogue that is easy to understand and follow
-The heroine encounters multiple loves scenes between the guys she interacts with

Hi My Sweet Heart and Devil Beside You are pretty similar.
-Both shows feature Rainie Yang as the lead actress in the romance story
-Both are slow paced, and use common Taiwanese phrases and dialogue
-Both feature the heroine encountering romances with several male actors

Shy, unpopular male lead and charming beauty. Pretty much the exact same premise.