This is a letter that Nobunaga wrote to Kobayakawa Takakage and Mori Terumoto in late 1573.
Passage comes from Jeroen Lamers's Japanius Tyrannus:
(Lamers p. 97-98)
"I forced Yoshikage to commit suicide and sent his head up to the capital. I took the majority of his remaining troops into my service, and with the whole province [of Echizen] being pacified, I ended my campaign there. I left behind district heads and quickly returned to northern Omi on the 26th [22 September]. I immediately attacked the castles of the Azai on the night of the 27th, which I captured the next day; I took the heads of father and son Azai, which I also sent to Kyoto so that the people of that town and its environs could admire them. It was due to the manipulations of the Azai that the Takeda from Kai Province and the Asakura clan from Echizen Province became my enemies in recent years. The Azai were also to blame for the treasonous ambitions of the shogun. You cannot imagine my happiness that I have slain them all, for I hated them deeply. If this current situation prevails, I will [shortly] incorporate Kaga and Noto into my domains. I have been on good terms for many years with Uesugi Kenshin from Echigo, so there will be no problem. As far as the Northern Provinces are concerned, they are completely under my command. Shingen from Kai has died from a disease and his succession will be a difficult task."
The heads of Asakura Yohikage, Azai Hisamasa, and Azai Nagamasa were sent as proof and a warning to those who are against Nobunaga. Proof that the three are dead and the Kyoto population can see the truth for themselves the bloody trophies. The warning was direct and head on. If were an enemy of the Demon King, this is the treatment you will receive. In the end, it was a perfect example of psychological warfare.
Tenka no tame!