everytime a manga sets the time traveller premise so close to the world wars it makes me feel bad about the characters lol

I hate that we "know" how this is gonna end thanks to the flashforward in chapter 1 (I absolutely hate flashforwards) yet I still hold hope it's not going to happen...

I have the feeling this manga got rushed and wasn't mean to be like this, it developed slowly and well for like 10 chapters and all solved in the 2 last ones is kinda... I wanted the poly ending to be honest