Xero you said it very good!!!
BioBushman, im disappointed my friend. Why did you think that Jman's death was in vain?
I think that it is necessary for some of the good guys to kick the bucket in a manga, it just shows that its not always the good guys that win a fight.
I think there is much more to jman's death, like most people said already, and I agree to that, is that Naruto needs to realize that its not a perfect little world, and that he can get past that comfort zone, where he is in currently. To realize that he needs to "protect" and take up more responsibility.
On the technical side, I think that the people must not just stare at the message that was written on Pa toads back. The fact that Pa and Ma toad was with Jman when he fought Pain makes a major difference, they have seen some of pains tricks, and knows how he fights, thus Pa toad had the ability to train Naruto to counter those techniques. Giving him more of an advantage than what J had.
I think the Jmans death also affected Tsunade's point of view. It was a major blow to her. I think that she might have matured more from Jmans death than Naruto

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Well all in all I liked the Jman, and he is a very skilled Shinobi, that gave hope to alot of people, and his death inspired alot of people to become stronger ect Tsunade and Naruto, I also think Kakashi. And it is needed for the Manga to take a more definite twist. Where you get a teacher teaching a student, the student turning roger. The teacher teaching another student. The previous student surpassing the previous generation by killing the teacher. And the grand finale, the two students good and bad facing off to see who is the strongest.
Brilliant!!!