Both of them are Republican era dramas ,, Both have amazing Bromance or Brotherhood relationship ,, Both have the same painful stories of this era fighting the corruption ,, a lot of killing and action scenes in both dramas
Both you will feel how strong relationships can be formed without having it to be blood related or romantic aspects
I loved Both dramas so much

A cop from the 80s goes into a tunnel comes out thirty years later to solve an old case
Quite similar synopsis for both of them
Retro detective didn't air yet but from the synopsis they are similar and Tunnel the korean drama was amazing one ,, you should gave it a shot

Similar of the ability to read minds also the male leads falls ill every time he reads people
,, it's non romantic though

similar bromance story with great chemistry between the two male leads
also both in republican era<<<<