Souga features exclusively in the spin-off series "Hokuto no ken Raô gaiden: Ten no haô", not within "Shin Kyūseishu Densetsu Hokuto no Ken: Yuria-den". Within "Ten no haô", he emerges as a key ally to Raoh, heir of Hokuto Shinken. Souga directly assists Raoh, alongside Reina and the enigmatic Sakuya, in constructing a hegemonic empire. His role centers on supporting Raoh's ambitions to validate a philosophy of conquest achieved through dominance and power, positioning Souga firmly within Raoh's inner circle during these empire-building efforts.