After the betrayal of Akechi Mitsuhide which led to the death of both Oda Nobunaga and his heir Oda Nobutada, Morimasa sided with Shibata Katsuie over making Oda Nobutaka (the third son of Nobunaga) as heir to the Oda clan whereas Hashiba Hideyoshi (later Toyotomi Hideyoshi) supported Lord Sanboshi. Sanboshi was the heir to Oda Nobutada and was still an infant at that time. This argument led to the split of the Oda clan retainers into the two main factions led by Shibata Katsuie and Hashiba Hideyoshi.