Both dramas revolve around hospital/medical settings.
The leads start on the wrong foot, yet they soften over time.
Both have comedic elements and are warm

In Both dramas the leads are acquainted in the past( L&P leads are lovers in college but MLH the ML has an unrequited love since childhood)
My little happiness is sweet and fun, while lighter and princess is a little dark and thorough
The leads are reunited while they are older and become colleagues

Both dramas are about young lovers who are separated because of life mishaps but keep loving each other despite the separation
In both dramas the leads meet again when they are adults and reconcile
The leads in both have somewhat complicated and heavy pasts

Both dramas are set during school/college days
The leads have a love-hate relationship at first that turns into romance
The leads are separated due to mishaps showing up but keep loving each other and meet up again in the future
The characters in both have heavy baggages from their past and have been through trauma
The leads become colleagues too

Both dramas revolve around school and college days
The leads fall in love while at school
The leads are separated due to mishaps and are later reunited
Past love cannot be forgotten sort of dramas
Both give off warm vibes

typical body swap dramas
the leads are in a relationship and have to live with bodies switched
TDOBY the swap returns to its original body but in Kojinsa Arimasu the story is a bit different

The leads switch bodies and look for ways to come back to their original bodies.
In the secret garden the Leads fall in love, but in Kamisama no Ekohiiki the leads don't fall in love but cooperate to return to their original forms

Both revolve around body swap and the original owners of the bodies exist at the same time
Eternal love has time travel too, but KNE doesn't have time travel

both show polygamy in different settings
but the roles are reversed, one the husband has few wives, the other one the wife has 5 husbands

Both revolve around polygamy
Hare-kon is less dramatic and more comedy, but Raise the red lantern is thorough and goes in-depth to show polygamy

Both dramas focus on Contract marriage without any previous knowledge of the other party, yet for personal reasons to fulfill the expectations.
The leads fall in love during the contract.

Contract relationship is the main focus in both dramas.
The leads are not so fond of marriage, thus they enter contractual relationships for personal reasons.