Both dramas masquerade under the guise of a classic revenge tale to tell a bigger, yet more personal story. They both focus on two male leads who have been connected through childhood (and there are many other similarities that would be spoilers).

Synopsis is pretty similar. Police man (or police related man in Age of Legends) goes undercover in a criminal organisation, gathers information, loses memories and the only evidence is in their memories.

Both tackle the idea of undercover cops in criminal organisations, but end up becoming brothers with the criminal they're spying on.

Many differences between the two, but one similarity is:
Main character getting dragged into a world of blood and murder unintentionally.

Both have (very) smart male leads. That's about it, but they have a similar.. atmosphere you could say.