This is all from one source, so there may be inconsistencies or mistakes. Must research further to confirm all the details. Still, much of this is quite fascinating.
A sidebar in a book on Nobunaga led to some fascinating information on the Ikeda clan, of Himeji Castle fame. Nobunaga's foster mother was of the Ikeda family, who at that time were in Mugi-gun in Mino Province. She had a son who was two years younger than Nobunaga, named Tsuneoki. (Also called Nobuteru.) Obviously he and Nobunaga grew up together, and it should come as no surprise that Tsuneoki was one of Nobunaga's earliest and most loyal supporters. It was he who executed Nobunaga's brother Nobuyuki.
When Tsuneoki was 10 he presented himself to Nobunaga's father and begged to be allowed to serve as a vassal. The formal clothes he was wearing at the time were Nobunaga's, and had the butterfly crest used by the Oda. After this time Tsuneoki used the butterfly as his crest. This is why the Ikeda use the butterfly crest, as seen everywhere at Himeji Castle.
Tsuneoki served at most of the famous Oda battles -- Okehazama, Anegawa (after which he was granted Inuyama Castle), Nagashino, he subdued Araki Murashige, fought the battle of Yamazaki where Akechi Mitsuhide was defeated, and Shizugatake -- though for Shizugatake he was on Hideyoshi's side. Clearly he was a trusted and relied-on general of Nobunaga's.
Wikipedia lists his remains at the Gokoku-in at Myoushin-ji, in Kyoto.