Reborn

Both are dark crime dramas. Both leads are capable and cool-headed detectives (that have a bullet in their heads).

Male Leads in both shows suffer from sequelae of being shot in the head, trying to live long enough to uncover the truth behind their assaults

While these shows represent two different genres (To Be a Better Man is about Friendship, and Reborn is a crime drama), both depict severely depressed men who strike up a friendship with orphaned girls.

Both productions star Zhang Yi as ML who befriends a teenage girl he once had an enemy-like relationship with.

Same male lead
different criminal case
same production company
same action criminal genera
both are enjoyable to watch

Both productions are set in the same "universe" with Guan Hong Feng (ML in Day and Night) being a supporting/guest character in Reborn.