The kata for Ivory Dagger is apparently イーボンダガー Ībon Dagā. That doesn't sound like "Ivory" at all, which would most likely be written as アイボリー Aiborī. The only possible romanizations I can think of would be "Ibon", "Ivon", "Yvon" or "Ybon", "Irbon", "Irvon", "Irubon", "Iruvon".