Izuna Uchiha

was a shinobi of the Uchiha clan. He along with his brother Madara Uchiha were renowned as the clan's two strongest members.

Background
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Personality
Izuna Uchiha was a harmonic and devoted person. He also appeared to be very competitive with his brother, Madara, in terms of skill. Tobi also implies that Madara and Izuna were close as brothers.

Appearance
Izuna was a fair-skinned man with long, black hair that had a blue tint to it and was tied in a ponytail. His bangs parted down the centre of his face to frame both sides of it. He wore the standard Uchiha outfit which consisted of a high-collared, blue shirt with the Uchiha Crest on his upper back and blue pants which were wrapped up in bandages at the ends. On his waist, he had a bandage belt that held a sack which presumably held ninja tools.

Abilities
Izuna was noted to be equal to his elder brother, Madara, in every way. Both of them had exceptionally strong chakra, even for Uchiha members and trained daily to hone their skills.

Izuna mastered his Sharingan at a very young age, alongside Madara. When Izuna awakened the Mangekyō Sharingan, his took the appearance of three bars stretching out of his pupil. When Madara took his eyes, the two Mangekyō combined. Izuna's loss of his eyes rendered him blind, but he managed to survive, and continued to battle. This sudden disability however, ultimately led to his death.

Legacy
While posing as Madara, Obito Uchiha claimed that Izuna's death after giving Madara his eyes played a great role in Madara's antagonism towards the Senju clan when they proposed a truce. Madara would have thought Izuna's sacrifice so he could stay strong and protect the clan as being in vain. Izuna's eyes continued to be of great importance, first, by granting Madara the Eternal Mangekyō Sharingan, and in his old age, Madara would also awaken the Rinnegan with Izuna's eyes. The same eyes were later transplanted into Nagato, who would later go on to become Pain, and a powerful figure-head of Akatsuki, and then into Obito Uchiha, who came to share Madara's ideals, and while posing as him, plunged the world into the Fourth Shinobi World War.

Trivia

 * is the name of a fox spirit in Japan and of a mountain. The latter is usually called Mount Iizuna, though. Iizuna, written with the same kanji, is also the Japanese name for the least weasel.
 * According to the databook(s):
 * Izuna's hobby was to train with Madara.