Ghosts theme is a main theme of two dramas. In both dramas one of a leading characters is able to see a ghosts. The seeing character in these dramas can protect themselves from ghosts by touching and being present with the other leading character.

Both dramas are happening in the same timeline. Beginning of both stories is the year 1997.
Main characters of both of the stories are a group of friends from the high school. Another similarity is that in both of the shows main focus is on the female main character's journey to pursue her passion. In Reply 1997 that's music and in Twenty Five Twenty One is fencing. Connection between main characters and following their life journey over the years is another of the resemblance in both shows.