A sixth season where Samurai Jack is on a quest to save Ashi and has to struggle between his moral obligation to keep the world safe from the evil that is Aku and having to bring back the Shogun of Sorrow to save Ashi, culminating in having to figure out a way to defeat Aku without sacrificing Ashi and having to explain to the Scotsman that he slayed Aku and is now trying to keep him alive.
Alternatively since time paradoxes apparently take time to go into effect, have Jack need to return to the future to save the world, since he could not defeat Aku without Ashi, and if Ashi can't exist without Aku, but Ashi helps defeat Aku, it begins to threaten existence as we know it.
