In his youth, Yukio possessed a typical complexion for a boy of Japanese descent, eyebrows, and short hair.
As an adult, Yukio was extremely tall, likely far exceeding six feet, as he was shown to tower over most adults and seemed to be a giant of a man when in the presence of school children. When compared to BlackWarGreymon, who is ten feet tall, Yukio was shown to be only a few feet shorter.
Following the death of his best friend Hiroki Hida and possession by Myotismon, his skin became unhealthily pale, he appeared to lack eyebrows, and he grew his hair out to neck-length.
Always something of an outsider, Yukio Oikawa was extremely lonely due to an inherent difficulty with connecting and communicating with other people. His one friend, Hiroki Hida was his only significant friendship. Hiroki's own father compared the two's relationship to that of one between brothers. It has been stated that it was the only time that Oikawa was truly happy. Even years after the death of Hiroki, the mere mention of his name is enough to bring Oikawa briefly out of his depression.
He was hopelessly fascinated with the potential of the Digital World, hoping to travel there with Hiroki, indicating an adventurous and more altruistic personality in his younger years. The two of them became fixated on the potential of what they could do there, especially in regards for what they could do for other people.
Following the death of Hiroki, Oikawa's depression took a steep dive, causing him to become nihilistic, cynical, and is implied to have even brought him to contemplate suicide. Following his possession by the remains of Myotismon, his personality became borderline sociopathic. He was ruthless, cruel, callous, and calculating in his actions. It was only in the presence of Cody Hida that remnants of his former self would surface, only be consumed by the darkness within him.
During his campaign of terror, Oikawa showed immense charisma, able to seduce Ken Ichijoji into a similarly cruel and self-righteous mindset following the death of his older brother Sam. This shows Oikawa's emotional intellect, as he was able to play off of Ken's feelings of misplaced guilt and immense grief. Despite his off-putting presence that was cited by many people, from acquaintances to coworkers, he had a natural charm that was difficult to deny due to his immense size, intellect, booming voice, and conviction in his plans and ideals.
Oikawa was also quite difficult to intimidate, as he did not shrink in the presence of even as dangerous a foe as BlackWarGreymon despite the overwhelming body count that his indirect creation had accumulated over the course of his rampaging.
In the end, with Myotismon's influence purged from his body, and being reunited with his partner, his more altruistic personality re-emerged, and chose to use the last of his strength to restore the defenses of the Digital World, redeeming himself and fulfilling his desire to enter the Digital World.
Digimon Adventure 02
In A Very Digi-Christmas,
- Based on his behavior and personality, it is likely that Yukio suffered from clinical depression.