I don't find it to be dark at all. Jack has to learn to accept that he lost but that there's still beauty and good in this world and so it's still worth living in.
this is exactly what I think will happen, and what I hope will happen. I posted that earlier in the thread and it was mentioned that that's basically how the comic ended, but I'm okay with that. It definitely seems like the direction that Jack's character is headed in, but I'm just basing that off the first few episodes I guess.
what I really want to happen, though, is this:
Throughout the season, Jack rekindles his connections with the people of the future, and gathers a new resolve to fight Aku, whatever it takes.
At some point, he'll begin to build a resistance, and at some point, he'll retrieve his sword. And then, he'll discover a temporary means by which to return to the past, and he'll have a short struggle with the idea that, in restoring his world, he'll be sacrificing his friends in the process. Nonetheless, he chooses to go through. but for whatever reason, he's not the one who gets sent through the portal with the sword. Ashi is.
Ashi returns to the past and defeats Aku in sick fashion. And then we're treated to an epilogue: Ashi acclimating to a beautiful world, untainted by Aku, where she enjoys the life of a wanderer; Jack, trusting that Ashi defeats Aku in his stead, comes to understand that his future still exists, and resolves to protect it and someday defeat Future Aku. eventually, Jack returns to the guardian portal at some point in the future. He defeats the Guardian in a short and unceremonious fight, but he's just there to look through the portal. He peers into it, and witnesses the restored world which Ashi is responsible for. Then, the scene through the portal changes, to the inside of the portal cave in the other time. The guardian lies defeated in the background, and a shadowed figure wearing a sword approaches the portal from the other side. The figure throws the sword directly at the 'screen' as though it's being thrown through the portal, and shit cuts to credits
like, it'd be nice if Aku gets his shit wrecked in both the past and the future, but I kinda want Jack to stay in the future, y'know? lol.