Ryusuke Nakamura's agency has announced that he will be appearing in Duke/Knuckle. (
Source)
Edit: Gaim Gaiden's twitter has announced more guests: Jun Toba will portray Kyoukai Inudou, Yggdrasil's head scientist and Ryoma Sengoku's predecessor, in Duke's part. In Knuckle's part, Maari will portray Azami, Peco's sister, while Ryusuke Nakamura portrays Neo Baron's leader, Shura. (
Source)
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