The Oniga Sigrogana War war was started by Tennou Myoga in an attempt to conquer the land of Sigrogana. For unknown reasons, the Tennou openly declared war on Sigrogana, stating his intent was to take the continent from the Empire. While the two nations fought equally for a time, in the end, it was clear that Sigrogana was the losing side, and the Emperor of Sigrogana went in person to make peace talks with Tennou Myoga. They did not reach an agreement, but despite the risk of meeting face to face, neither man was harmed in any way. Upon the Emperor's return to Cellsvich, the war began anew.

However, after that visit, something changed; the Onigan army could not gain a foothold and were continually pushed back, as if they had hit an impassable wall, and would not have any success in their conquest until the war was brought to an unexpected halt after Tennou Myoga's assassination. It ended peacefully soon after that, with Myoga's son, the new Tennou, Ang, engaging in peace talks with Sigrogana and restoring the two nation's relationship.