Both are about first loves who got seperated and meet again after many years.

In both dramas one side recognizes the other one first but can't tell the other.
Even after knowing about each other there are many obstacles stopping them from being together (e.g. other partners they got in the meantime), but their story and chemistry makes the viewer root for them to end up together.

Also both dramas have older leads (midthirties?) so for viewers who want to see more mature and not-so-childish romance, this might be good.
(And light spoiler - both have happy endings)

- both dramas are set in the broadcasting/entertainment industry
- both focus on the growth and relationships of the characters, but not too heavy, there are lots of funny scenes
- both have romance, but its not cheesy
- lots of characers (and many cameo-guests)

- overall feeling
- both have firefighters and paramedics as main characters
(but the MLs are different: First Responders - detective, D-Day - doctor)
- both deal with life-threatening accidents / disaster
- both have subtle romance