I wrote a review about the manga a while back:
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Well rarely a main character changes fundamentally from how he was at the start of the series. Luffy, Naruto, Ichigo... all of them are largely still the same. Kenichi never really lost his completely his timid cowardly nature as that's a part of who he is, however he becomes in the end a dependable strong person. The entire point behind is to overcome such things as cowardice, but not forsake them either as to remember who he really was.
And as why many characters are 'non bad ass with a cool attitude' well it's because, believe it or not, perfect characters are not intriguing. It's one of those things I pity people for who have that urge to proclaim their favourite character as the strongest, most perfect character in existence. It's easier to feel familiar with someone who has flaws rather than with someone who has none whatsoever. Also in Japan an entire generation was inspired by a goofy kid named Goku, so it's no surprise that many characters are similar to him.
