Both of them have Joseon kings falling in love with girls from the future and both of them have time traveling elements. The big difference, however, is that in Rooftop Prince, the king gets to travel to the future while in Splash Splash Love, the girl gets to travel to the past (Joseon). They are also similar because of the reincarnation/past life elements (people from the past are also in the present time but have different identity).

Both films tackle the same thing: the struggle of a single man taking care of a child he barely knows. Usagi Drop is a little bit in the dramatic side while Baby and I is a little bit in the funny side, in my opinion. And the little difference is that the child in Usagi Drop is six years old while in Baby and I, the child is still an infant.

The story of Zettai Kareshi revolves around a girl who is given a free trial to use a lover-type robot, Nightly 01. It has its fair share of quirks and cool scenes. It is also the same as Absolute Boyfriend, the Taiwanese version of Zettai Kareshi (however, the female lead here is Korean so the dubs might be disappointing).