Diabound is a character in the Yu-Gi-Oh! manga. It was Bakura, King of Thieves's ka, created by the spirits of the slaughtered town of Kul Elna desiring revenge and it had the power to absorb the abilities of other ka it defeated. Its form evolved as its powers grew.
Diabound is first Summoned when Bakura entered Pharaoh Atem's palace in his first attempt to take the Millennium Items. Everyone present is shocked by the strength of Bakura's hatred and that Diabound is actually a holy spirit, which Bakura claims is due to his loyalty to his cause. Priest Seto ignores the spirit's strength and attempts to seal Diabound in a stone tablet with his Millennium Rod, but Diabound breaks free with ease. Unfazed, Seto instead Summons "Galestgoras" to Duel Diabound. Galestgoras battles well, but Bakura uses the special power of Diabound to shatter the tablet that Summoned Galestgoras. He then has Diabound engage in battle with the other ka Summoned by the Priests and easily overpowers them. Atem, after reclaiming his father's mummy from Bakura, Summons one of the three Nameless Gods, "The God of the Obelisk" and soon Bakura finds himself on the receiving end of an easy overpowering. Despite his loss, Diabound is able to survive and Bakura escapes.
Bakura later Summons Diabound when Priest Mahado, bearer of the Millennium Ring, leads him into Akhenamkhanen's tomb to Duel. Despite Diabound having evolved into a new form due to Bakura's hatred becoming stronger, inside the tomb, Mahado's "Illusion Magician" is able to fight at its full power and the two battle evenly. Bakura eventually triggers one of the tomb's traps and kills Mahado, but the Priest fuses his ba with Illusion Magician into the "Dark Magician" and attempts to destroy Diabound for good.
Bakura survives again, and infiltrating the Shrine of Wedju to attack Akhenaden, he has Diabound, whose form has evolved yet again with the acquisition of the Millennium Ring, use its phasing power to destroy the stone tablets before Akhenaden can Summon them. When he flees from the Shrine, he Summons Diabound as the Pharaoh pursues him with "Slifer the Sky Dragon", another of the Nameless Gods. Despite its power-up, Slifer retains the advantage, until Bakura begins attacking the townspeople, forcing Slifer to defend them, not only taking the attacks but also restricting its movement. Diabound hides with its power and nearly kills Atem, but the Priests intervene and rescue him. Diabound defeats Slifer when Atem sacrifices it for a chance to win, but is saved when Bakura has Illushu intercept the attack of Duos. Bakura takes the Millennium Puzzle from Atem and leaves him for dead after throwing him from a cliff.
Atem survives, coming to Kul Elna to reclaim the Puzzle and defeat Bakura. Bakura Summons the again-evolved Diabound, and the Pharaoh is defended by Mahado in the form of Dark Magician. With Diabound handicapped protecting the Millennium Stone, the battle proves to be largely even, but Diabound resists repeated attempts to slay it and phases into the walls. Shada's attempts to find it prove unsuccessful until Atem has Mahado open up holes in the ceiling to let light into the chamber and reveal Diabound. Diabound is able to survive when Bakura has the spirits of Kul Elna form a protective shield around it. The Priests arrive to save Atem after Shada is injured and Bakura takes the Millennium Ankh, causing Diabound to grow in strength. They Summon their ka, but Diabound once again overpowers them until Kalim has the idea to use the Millennium Scale to combine the ba of two ka, Duos and Curse of Dragon, into Duos Dragon. The fused ka proves to be an equal to Diabound when enhanced by Mahado's magic, but is unable to break through the shield. Bakura seizes his chance to kill Kalim and take the Millennium Scale, seperating Duos Dragon, but the attack did indeed break the spirit shield and Mahdo finishes Diabound off with his strongest spell. With Diabound's destruction, Bakura slowly dies as well.
When Dark Yugi enters the world of his memories to relive the events of his death, he replays his battles with Bakura and Diabound. In a departure from the original events of history, Yugi Mutou reunites with Dark Yugi and replenishes his energy after the destruction of Slifer, allowing the Pharaoh to Summon "The Sun Dragon Ra" and destroy Diabound with its Egyptian God Phoenix form. The spirit of Akhenaden, claiming to be Zorc Necrophades, then appears to rewind time as the first use of Dark Bakura's ability to control time in the Shadow RPG, and Diabound's destruction is undone, with events playing out from that point as they had in history.
Due to Bakura's loyalty to his village and his cause, Diabound is actually a holy or god type spirit. However, due to the fact that Bakura's hatred is what increases its strength, it later develops into a more demonic form.