"Kira is childish and he hates losing...

First off, I think it's a shame that Mello died the way he did and honestly if it hadn't been for Mello, Near would have never caught Kira. Mello and Near were both extremes of L's personality. Near the stoic, anti-social side and Mello the emotional side. The creator took those and made them slightly more extreme for each character. Near said it himself at the end of the series. Neither he nor Mello could have surpassed L alone, they had to do it together. I don't like Near but, that's not the point. Mello was obsessed with being better then Near because they were put in a predicament where they HAD to compete with each other at the orphanage just to be in the spot for number one in line. It's sad but there's nothing we can do about it since that's the way the creator of the series wanted it to be.
I'm also childish and hate to lose. That's how I know."