Musashi was one of the Overmaster's Cadre.

Synopsis from Justice League International Vol 2 63: Metamorpho's powers have been changed by his encounter with the Family, and he can now absorb elements from objects he touches. He is concerned that he may cause massive destruction if he doesn't keep this in check. Crimson Fox reveals her identity to him to explain why it seems that her feelings for him have changed - she does not share her twin's emotions.

Later, Metamorpho, Maya, Power Girl and Lionheart assist with relief efforts following an earthquake in Nepal. Here they encounter a young boy with similar powers to Maya's, but he dies when he speaks to them of the Immortal of Saba. Metamorpho gathers the rest of the JLI and they converge on the African jungle, discovering a majestic hidden city full of advanced, yet ancient-seeming machinery. Here they encounter a number of powerful men and women from across the world along with their leader, the Immortal, who has somehow converted Maya to his cause.

Exerpt from Scribblenaughts Unmasked: Musashi is a Japanese warrior who was duped into following a villainous agenda by an alien called the Overmaster.