So far I have to say that it has been very nice to read, the only thing that annoys me is that the training and missions lack detail, you could put a little more "color" to them.
Here's my opinion, if you want it to seem more realistic like in Kengan or Kenichi, change the training a bit, like what kind of training he receives, no one, I repeat no one malnourished arrives and carries a military backpack with 40kg on his back, make a kind of adaptation in the training if you want to make it more realistic, as we have an elementary school boy (if I'm not mistaken) on average children finish at the age of 14, apart from the fact that he possibly doesn't eat well (pure rice doesn't contain everything a child needs to grow, so he's a bit malnourished) make it an arc of growth and adaptation, I don't know, it's your work.
But if your goal isn't to be realistic, you're doing fine.
