Farewell, Black Cat

Soji Okita only exists as an ally on the pro-Shogunate path - side against the Shogun at the Kyoto branch and he dies, taking this with him. To save him, recruit him (he becomes available after the main mission "The Shogun's Journey to Kyoto") and clear his Bond missions, which centre on finding medicine for his illness. Picked the other side or missed his bonds? Replay via the Testament of the Soul on the same save - which is exactly why this is not a true mutex, nothing's permanently lost.