I started learning Japanese about 2 months ago and today, while talking with a friend of mine who has been studying Japanese for about two years, he gave me this example scenario about は particle and the 'contrast' it creates; and it confused the hell out of me:
Imagine a group of people conversing. One of them asks the entire group what are their nationalities. Half Japanese one says he is Japanese by saying: 私は日【に】本【ほん】人【じん】です。And right after him another Japanese guy says the exact thing too. The half Japanese guy feels offended.
Now, the reason the second guy's answer offended the first guy is, he implied that he is more Japanese than the other one. If he didn't wanted to imply that, he could just use the も particle instead of は. Because after は, you state something that is lacking in the previous 'topic'.
But I read in an online source that the が particle puts the focus on the the word it attaches (subject) while は puts the emphasis on the part that comes after it. And that source, as an example, stated that if someone said これはぺンです while holding a book, you would point to a real pen and then say いいえ、これがペンです Which would mean: No, this is a pen.
Is the example my friend gave me about は particle correct? Shouldn't there be が instead of は for the second guy to mean "I'm the Japanese one!"?