Help with the syntax of a sentence.

Greetings

Long ago, Toritobe helped me with the translation of a line from a movie for which I am very grateful.

Now, I'm trying to understand its syntax.

The line it's the one of 1:10:30 to 1:10:35 in this video:

https://www.youtube.com/watch?v=7obFlaRzAe8
(Please ignore english subs, are wrong in that line.)

And written:

士郎の理想、英雄となった姿があなたではないのですか。
Shirō no risō, eiyū to natta sugata ga anata de wa nai no desu ka.
You are the figure after Shirō became a hero, which was his ideal, aren't you?

My questions are:

- That "ga", for what it is used in the line? To say that "the ideal of Shirou is the figure that became in a hero" or to say "You are the figure, aren't you?" ? What is the correct method to follow to know?

- How do you know that it's "Shirou" who became a hero, and not the "figure" or the "ideal"? (Apart from the context or meaning, I wonder if there are also some method to follow to know.)

- Japanese people fully understand this line the first time they hear it? is not something difficult even for them? I think it's a little complicated. (Just curious.)

Sorry for the inconvenience. If you could help me clarify this I would greatly appreciate it,. Thank you very much.

Shirou said:

- That "ga", for what it is used in the line? To say that "the ideal of Shirou is the figure that became in a hero" or to say "You are the figure, aren't you?" ? What is the correct method to follow to know?

Click to expand...

が indicates the subject.

姿があなただ。
The figure is you.

Shirou said:

- How do you know that it's "Shirou" who became a hero, and not the "figure" or the "ideal"? (Apart from the context or meaning, I wonder if there are also some method to follow to know.)

Click to expand...

It must be 姿が英雄となったもの if "figure" is the subject of なった, and must be 理想が英雄となった姿 for the case "ideal" is the subject.

Shirou said:

- Japanese people fully understand this line the first time they hear it? is not something difficult even for them? I think it's a little complicated. (Just curious.)

Click to expand...

Of course, yes.

Thank you very much, that helps me a lot!

So how do you know that the subject of "なった" is "士郎"? By elimination? Because the particle ga is not usually used with living beings and "士郎の理想" don't have "が particle? Or with other method?

I think I'm finally starting to understand everything, I just need to clarify that.

Thanks again.

all of those (Except the particle ga is not usually used with living beings. This is completely wrong.) + the biggest factor "from the context" (It is stated previously in the story that Shirō's ideal is to become a hero, no?)

Yes, that it's right. Thank you very much for all, Toritoribe.