It is difficult to understand the complete context of a war until well after the war is over. The Spanish American War is infamous for its yellow journalism that was used as propoganda to tilt American perspectives toward a war against Spain. Propoganda said the war was declared in order to fight for Cuban and Philippines independence against Spainard exploitation. The truth was that the United States wanted to determine trade in the Carribean on their terms and very little consideration for what the populations of these countries wanted in their governments. Just two days after the Philipines gained their independence, a guerilla war was waged between the Philipines and the United States. The war resulted in the deaths of 200,000 Filipinos and the destruction of the Philipines provisional government. None of the American soldiers knew this would be the result when they got involved. Tsyokute New Saga shows same sort of tunnel vision perspective through the use of time travel.
In Tsuyokute New Saga, a war between humans and demons was fought. Humans eventually won the war, but at a large cost of thousands of lives. The main character, Kail's losses are a microcosm of this tragedy as much of his home was destroyed as a result of the war. He succeeds in killing the leader and strongest enemy, the Demon King but is mortally wounded in the fight. Considering practically everyone including his wife, his best friend, and most of the people he knew died in this war he practically welcomes death. He passes out and wakes up to find his consciousness is in his past incarnation, four years before the war started.
What New Saga excells at is subverting the hero's journey. It's like Frodo going back in time, only to grab Gandalf's beard and shout "Summon the Fucking Eagles!" He uses his past knowledge to dig his way past a brutal dungeon to get the treasure underground. He acknowledges who were his greatest allies and wastes no time in trying to recruit them. This is one of New Saga's greatest strengths, the hero is portrayed as smart in a convincing way, without having to degrade the intelligence of those around him.
Yet while he is smart, he is also failble. He sees the war from a utilitarian perspective and has difficulty, differentiating people that were heroes in the future from their flawed present selves. In an early arc, he tries to recruit the knight captain, Zentos, a paternal figure to him during the war that was largely responsible for shaping him into the hero he eventually became. At the same time, he tries to rescue a princess that would become a better ruler for his country has she not died just before the war. Problematically, he finds Zentos trying to assassinate said princess and is forced to kill him. The tragedy of Zentos's story shows the potential drama New Saga has to offer. Zentos was a heroic figure in Kail's past timeline, but in the present, he died the dishonorable death of a traitor and that's all he'll be known for. What's more, none of his friends can understand why this affects Kail so personally.
However, in another arc he finds a girl, Minagi, whom he always saw as sociopathic killer, as an affable if brutally honest destitute. She is an assassin by necessity, yet due to the unintended consequences of Kail's actions, he inadvertently stops her from becoming a remoreless killer. Morality in New Saga is often governed by circumstance, and its Kail's knowledge of the future that disrupts these circumstances for better or worse.
All the while there is an arcing mystery over why the war occured. Kail has little understanding over demon society and is confused by their motives and ideals. The story builds intrigue as he finds demons acting as spies or manipulating conflicts between humans. These details give small hints that suggest the demons are more than just an evil, destructive, force.
Action scenes are decent enough. Anime tropes like flash step can be annoying for people that prefer choreography in their fight scenes. However, the creators always make fights challenging for the main character, as Kail often fights opponents that are much stronger than the weak body that he currently inhabits. He often has to outsmart his opponents, plant traps and anticipate their actions as oppose to overpower them with physical force.
I have some minor gripes about the story. It is a harem, though it does balance the gender ratio with some strong male characters. It contains some of the problems with harems, including the female characters being really attached to the protagonist with little justification. The childhood friend character isn't well characterized and due to most of the cast being physical fighters, tends to fade into the background during conflicts. Hopefully, they will have a better balance of romance in later parts of the story. The art isn't very impressive either, backgrounds are often left blank, characters bodies sometimes have wierd angles, and it could really use more shading. People that like art from Tokyo Ghoul or Shingeki no Kyojin will see New Saga as a bit of a downgrade.
All in all, I like New Saga, as it shows both war and people as complicated. Kail's past timeline provides a background to characters without completely establishing them. Conflicts occur not just between Kail and other characters but also Kail's future perspective and the events that happen in the present.