Spaw - nice summation on Colin Kelly and Saburo Sakai. Here are a couple more details. I believe it was the Ashigara, a heavy cruiser, which Kelly did a bombing run on. It did not get sunk, nor did any other Japanese ships on that occasion, but Kelly certainly gave it a try, anyway. His B-17 was of an early type, lacking a rear gun postion at the end of the fuselage (though it had waist gunners), and Sakai was able to get right behind the tail and fire enough rounds to bring down the plane. Japanese fighters usually had great trouble shooting down B-17's. They later found, like the Luftwaffe fliers, that the head-on attack worked best.
Sakai was officially credited with 64 victories, as Spaw indicated. The highest scoring Japanese pilots were Nishizawa and Iwamoto, both around a hundred victories. The Japanese were very stringent about awarding official victories, so it's hard to say what the real combat score of any of these men was. They weren't sure themselves, in the heat of action, whether some of their damaged foes made it home or not.