Well then this was one hell of a masterpiece considering just how innovative the author got with the story. It really sells the idea of how Seija can be seen in two different lights. The only difference between the 1st and 2nd story is the arrangements of the panels themselves being in the opposite direction. While it isn't perfect in that in some ways the 1st story can seem rather confusing when reading, with some of the panels seeming to be, for lack of a better word, forced into that sequence, it does indeed help to portray that the inverted side of the story. From Seija being a murderer to being a rumoured hero. It is a really impressive piece of work that should be explored more. You can read the summary by ADT555 above^^ for the story itself if you haven't already.
In a way this story kinda reminds me of one of those videos where the words are all in lines. When each line is said, from top to bottom, it is to represent the attitude and beliefs of a particular person. Now when that is finished the quote is then read in the opposite way, from bottom to top. From there it seems to show a different person saying the same lines but in the opposite sequence. Through this it can seem to portray a completely different kind of person as compared to the one earlier, despite lines never having been altered, only their sequence. In this way it shows a change in personality or attitude towards a certain subject matter.
I don't know name for these kinds of ideas, and if anyone does it would be grateful if you responded to this comment.
Video link: https://www.youtube.com/watch?v=lFz5jbUfJbk
All in all though this doujin is one heck of a treat to the eyes. It may seem confusing at first but once you are over that hurdle, it really is a masterpiece!