S1·E4 Attack the Bloody Cross! The Secret Technique, Death by Soft Strikes.

Ken learns that the prisoners that were transported with Rin were taken to a prison camp in a nearby valley. Ken manages to break the imprisoned villagers free, but during their escape they're all slaughtered in an ambush led by Mr. Heart, the last of the Four Jacks. While Heart's excess flesh proves resistant to his attacks, Ken eventually uses a techniques which penetrates through his body. From his battle with Heart, Ken learns an important clue which reveals to him the identity of King.