Well done, great art style, tough action and more story than I had expected. I followed your game progress from the beginning on the discord - impressing how polished it looks at last.
To answer the question of NitroSodium: Shōsa (少佐): Military rank of major or lieutenant commander. An obvious reference to the main character. And yes, the background story is not entirely new, as Mentel said :-) The dialogue speed could be 10% slower.
All in all, a very rounded and complete game.