This is a pretty close match between these sword fighters. Seishiro has always shown himself to be a very exceptional fighter and the Tsubasa series does imply that Seishiro may still have the edge. That being said, he still is a little slower than Syaoran and the kid is a quick study. I like to think that he could win with pure skill to make up for his lack of physical strength, but it would be a close battle. Syaoran wins.