The last season had an entire episode dedicated to the difference Jack had made in the future, that hope was not lost for the world, despite Aku's evil
Even in the rest of the seasons, Jack repeatedly missed or gave up on opportunities to return to the past because he decided saving someone immediately was more important
But no Jack has to return to the past cuz the theme song sez so lolololol
The entire asspull of Ashi having akus powers and also she can send him back to the past was dumb as hell
The stupid fucking wedding scene, which totally forgot that Jacks parents were elderly and decrepit when aku sent him to the future, and also Ashi has to disappear because muh feels
And nevermind the fact that in the birth of evil special, the sword was shown to not be able to permanent destroy aku, and only seal him away.
The entire fucking thing was a trashfire>ASHI, I LOVE YOU