Ouroboros (2015)

Both dramas feature a policeman and a member of the Yakuza who are allies in the quest to find out what happened to a woman they were both very attached to.

In Ouroboros they're siblings in everything but blood, and in Kei x Yaku what they have is closer to a romance.

while the plot line is very different, both are action packed and suspenseful. After watching Bloody Monday I was anticipating another show that could have as much adrenaline and suspense. Ouroboros is the only other show so far that has come close to being as awesome as Bloody Monday.

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).