It's kind of a pity the first chapter has to sell the edge already, so the manga couldn't run chronologically. If we had had 15 chapters of normal hero stuff, with the sister, her husband, and the hero's companions introduced properly and built as characters, plus the princess first appearing normal and bright, along with the knights and such, all the deaths and betrayals would have carried an actual impact. There could have been tiny hints here and there, but there might also have been some red herrings. A capable author can also pull off things like Helck did. But the format of these extreme revenge stories is as it is. It can't be helped.