Bossender is a mythical sword wielded by Ione which she received from Entity just before the Crash. It's use is still unknown today and Ione remains mysteriously vague in the series, with not even Kolbert knowing of her whereabouts. It is one of the 12 weapons forged by Entity.
Bossender resembles a longsword, with a thin blade constructed of Orical. In the brief shot seen of it in Quest Mode, the blade looks almost complete, implying Ione has had more luck finding the shards of her blade than Kolb with Critbringer. Runt has a brief encounter with Ione(this is not 100% confirmed, but there was a different photo that clearly stated that the person in the picture was Ione, and Ione looked nearly identical to the girl that Runt found) in 8BW5 while he is on his way to Owl's Reach.