Well, as far as I recall...the tsurugi refers to the straight, double-edged sword that the japanese used prior to the emergence of the saber-esque tachi and katana(when bows, not swords, were the more prominent weapon, I think). I seem to recall pictures of warriors in armor with straight swords and the large bows (daikyu) while on horseback ....I could be wrong, though. As for the kanji involved...I really don't know.