What are clouds,
But an excuse for the sky?
What is life,
But an escape from death?
~ Yabu's death poem.

Kasigi Yabu is a character from the Shōgun novel and television mini-series by James Clavell.

While appearing to be loyal to his Lord Yoshi Toranaga in reality Yabu was only loyal to himself, willing to play the powerful men seeking to control Japan off against each other so that whoever won he would gain more power. Yabu would often work with the Jesuits and Portugese visiting Japan in order to cement his own position. He would soon betray Toranaga in favor of Toranaga's rival Ishido Kazunari

When John Blackthrone and his ship the Erasmus first arrived in Japan Yabu saw an opportunity to take the weapons and treasure from the ship. After boiling a member of Blackthrone's crew alive he was able to secure the cooperation of Blackthorne. However Toranaga learned of this and sent his General Hiromatsu to take charge of the Erasmus and her crew in order to have leverage against his main rival on the council, Ishido.

After Blackthorne was moved into Toranaga's castle Blackthrone was soon attacked by an Amida Tong assassin. Being one of the few men who knew how to hire such an assassin, Yabu fell under suspicion and was summoned by Toranaga the next morning to watch the sun rise with him. The message was clear that Yabu was on probation now.

Blackthorne moved into a village in Yabu's territory, where he was to learn Japanese with the help of Toranaga's translator Mariko. Yabu threatened the villagers with death if Blackthorne did not learn Japanese in six months, in response Blackthorne nearly committed suicide in protest. Impressed with Blackthorne's willingness to sacrifice his own life Yabu stopped Blackthorne from committing suicide, having a newfound respect for the European.

When Mariko and Blackthorne travel to Ishido's castle to force the release of hostages, Yabu killed Captain Yoshinaka - the official in charge of the castle's defense. A group of ninja hired by Ishido Kazunari and Yabu attacked Mariko and Blackthorne. When they locked themselves in a room with a heavy metal door, the ninjas used explosives to dislodge the door. The explosion killed Mariko and severely injured Blackthorne. (In the novel he lost his hearing, in the TV miniseries he lost his sight). Blackthorne later recovered from his injuries.

The two samurai who had been guarding the room where Yabu murdered Captain Yoshinaka came forward to inform Hiro-matsu and Toranaga of what had happened. With Yabu's treachery revealed he was summoned to a meeting with Toranaga. Toranaga asked him to explain why he had felt it necessary to kill Yoshinaka. When Yabu angrily demanded to know who accused him Hiro-matsu waved the two samurai forward. Yabu realized at that moment that he was found out. Toranaga let his falcon do some talking before ordering the daimyo to commit seppuku.

Numerous samurai - including Blackthorne - gathered to witness Yabu's seppuku. As one of his last acts Yabu gives Blackthorne his sword, feeling that Blackthorne was the best man to take the weapon. After reading his death poem, Yabu proceeded to ritually disembowel himself, with Hiromatsu slicing off his head when signaled.