Kiyosu Castle

In the early spring of 1555, Nobunaga finally took over Kiyosu Castle, the jewel of Owari.  This was key since it was a major step in unifying Owari. He had some help with his uncle Oda Nobumitsu.  However, Nobumitsu did not live long after as he was assassinated by on of his retainers, Sakai Magohachiro.

Passage from the Shincho-Ko ki (The Chronicle of Lord Nobunaga) Elisonas and Lamers, pp. 74-75

"In Kiyosu Castle resided the deputy military governor (shugodai) of Owari, whose name was Oda Hikogoro [Nobutomo].  Saki Daizen, a major land owner, was his assistant deputy governor (koshugodai).

Now that Kiyosu's other leading figures--Sakai Jinsuke, Kawajiri Sama no Jo, and Oda Sanmi--had been killed in battle, Daizen could not hold the castle against Nobunaga on his own.  He therefore begged Lord Magosaburo for help, in return offering him the joint occupancy of the deputy governorship with Lord Hikogoro.  A deal was made.  In compliance with Daizen's wishes, Lord Magosaburo sent him an elaborate written oath that there would be no double-dealing.
Accordingly,
On the 19th of the Forth Month, [Tenbun 23 (1554)], Lord Oda Magosaburo of Moriyama moved to the southern watchtower of Kiyosu Castle.  On surface, all seemed to be as it should, but in fact Lord Magosaburo had made a secret compact with Nobunaga to play into Kiyosu's hands.  In return, Nobunaga pledged covertly to partition Owari's lower four districts, more or less along the line of the Odai River, and share them with Lord Magosaburo.  This Lord Magosaburo was Nobunaga's uncle.  The lower half of Owari Province was divided into two parts called "west of the river" and "east of the river," consisting of two districts each.  So two districts would go to the nephew and the other two turned over to the uncle.  That was their deal.

On the 20th of the Forth Month, an ambush was prepared.  Should Sakai Daizen come to the southern tower to pay hos repects to Magosaburo, he was to be killed by men who lay in wait.  Daizen indeed came to the castle, but he sensed something dreadful in the air and immediately took to his heels, not stopping until he reached Suruga Province, where he asked Imagawa Yoshimoto for asylum. Magosaburo, however, forced the deputy military governor, Lord Oda Hikogoro, to commit hara-kiri, seized control of Kiyosu, handed it over to Kazusa no Suke Nobunaga, and moved to Nagoya Castle himself."

As mentioned above, Nobunaga's uncle Nobumitsu, did not live long after this event.  Once he was assassinated, Nobunaga handed Nagoya Castle to his elder retainer Hayashi Hidesada.  One has to remember that betrayal was very common during the Sengoku Era in a land where bloodshed was king.

Tenka no tame!