Was there any reference to Shigure's brother before Chapter 545? This chapter came to me as a real shocker. I always thought Shigure was an only child. As the title says, were there any references or perhaps even hints or foreshadowing that Shigure had a brother?
Since he knows Kosaka style, I want to say he's the biological son of her adoptive father, Hachirobe Kosaka. Pretty sure he alluded to his son being dead.