Board Thread:Editor Board/@comment-26391060-20131113175757/@comment-1173941-20131113182404

Aye, ALO allows kana characters to be used, as Kirito in Volume 3 said he'd use the katakana form of his name (though, the anime ignored that)

That being said, There are also games that allow you to input kanji as your name too. ALO hasn't been known to restrict this, though.