I'm not really sure, to be honest. I do know that in Japanese, names are typically written in kanji characters (see my signature), and that's how Kosuke's official website has it written. What've heard, however, is that they're just as often written in katakana characters, such as on that shirt. Someone better versed in the conventions of the language and the culture could tell you more. I would imagine, or at least hope, that a major apparel manufacturer and licensee of the player's association like Majestic did their homework on such a thing before putting the shirt into mass production (especially since I have that shirt :-").