It is said that Nobunaga did this because he remembered how taken Tadaoki had been by the Kuyo (nine-planet crest) motif etched on the hilt of his (Nobunaga's) short sword.
以前、忠興が信長の小刀の柄に九曜が描かれているのを大変気に入っていたことを信長が覚えていたためと言われる。