Both Female Leads are writers and kind of have a bold character, while both ML are hardworking and have a similar personality towards the FL.

These two dramas aren't similar if you do not consider the romance and some character aspects.

In Longing for You, a murder case occurs in Woojin, a town that doesn't have crime. Oh Jin Sang, joins the investigation team when his younger brother is identified as a suspect in a murder case, he later is cleared of false accusations, and the true culprit is revealed. The brother is suddenly attacked by someone on a rainy night and dies unexpectedly. In 'My Perfect Stranger', Yoon Hae-jun and Baek Yoon Young travel back in time to 1987, to investigate serial murder cases that happened in Woojung-ri , another town that doesnt have criminal activities. Hae-jun attempts to prevent his death in the future, and he and Yoon-young try to save people who are close to them.

*Only differences are that in 'Longing for You', there is no time travel, and that they aren't trying to investigate serial killings.