[Character Discussion] Matou Shinji

Shinji's not a worse person than Sakura is. He acted just like any arrogant person would act when put in such a situation. There's a reason Shirou says he's never been like this prior to the Grail War and Fate/Hollow Ataraxia confirms this with SoL Shinji scenes where he acts like a cool guy to hang out with, not to mention that Rider describes Perseus as ''Shinji who succeeded'', showing that Shinji is another victim of Zouken's actions and that he can be heroic in certain situations as well.

Him raping Sakura is also the result of the mentality he developed not only thanks to Zouken and his father, but also thanks to Sakura herself. In UBW epilogue - after the Grail War, it is said that Shinji and Sakura get along well as a brother and a sister.

How an ordinary person - that has no Magic training or anything else that puts him above the status of a normal person aside from knowledge on magic's existence - would react in such an extra-ordinary setting and how would his status as an ordinary person, being put in a comparison with extra-ordinary people, would shape his mentality and actions in order to correspond to the extra-ordinary setting is the point of Shinji's character.

Prologue and Fate do this by setting him as your average arrogant, popular kid at school who thinks he's better than everyone and is popular due to it - an ordinary person. UBW does that as well, and points out how he's the only one he thinks he's special despite being an ordinary person which is then a lead on in HF where his mentality is fully explained and it expands upon how his status as an ordinary person shaped itself in order to fit the ''extra-ordinary setting and expectations'' that his grandfather and the war ''expected'' from him.

He isn't meant to be sympathetic. While it was pointed out that he was a victim, it was never really pointed out how ''tragic'' he was like it was done with Lio's character - from Kara no Kyoukai, both are written by the same author and are a part of Nasuverse. He just had his role to give us a perspective of a normal person in the Grail War and that was done well.

Basically, Shinji's role in the story is more so to high-light Shirou's characterization and actions as some kind of a rival-like character, but at the same time, not exactly a rival-like character. Both Shinji and Shirou were raised as normal people - aside from magic knowledge and their own personal inner conflicts - so ultimately, they could - to a point - be viewed as normal people. However, as Shinji is some with no power who is constantly put in an extra-ordinary setting where he could die at any moment, we see how this brings out the worst of him and makes him more frantic and cowardly than he usually is.

This contrasts well with Shirou since unlike Shinji - another ''normal'' person - Shirou doesn't become cowardly and frantic, but instead becomes more suicidal in his heroic acts, showing us how far removed Shirou is from the sense of normal human function despite being raised in essentially the same way as Shinji. Unlike Shinji who becomes worse as a person to the point where he is afraid of his own life like a person would be afraid in a war, Shirou becomes more violent and suicidal just like a sword would in a war. It shows us how Shirou functions as a weapon more than a human.

So yeah, I think Shinji highlights Shirou's actions and mentality quite a bit as well.

Also, I like how Shinji and Shirou are very similiar in a sense. They both have a dual personality - with one personality being an ugly, dirty one that tries to become the ''ideal'' personality they have in mind.

In Shirou's case, he is a broken, violent person far removed from the sense of social norms and doesn't know what a Hero should be. That ''ugly'' personality of his tries to become the ''ideal'' personality that is the Hero Emiya Shirou, a person who acts under command of his ideals and is more machine-like than his actual personality. His ideal personality is that of Fate Shirou.

In Shinji's case, he is the arrogant, weak and talentless person who tries to become the ''ideal Shinji'' that everyone wants him to become by deluding himself that he is a Master who is capable of winning the war and bringing victory to the Matou family.

But neither of them can ever become their ideal personality. They can just try to replicate what their ideal personality is and the result is the personality that is neither their ideal personality, but still has habits of their ideal personality.

Shirou actually has three personalities - or rather sides or perspectives to his character -, but that's irrelevant to the topic.