|Dub Name||Sam Ichijouji|
|Family||Mother and father (Unnamed), Ichijouji Ken (Younger brother)|
|Voice Actor||Paku Romi (朴 璐美)|
Osamu Ichijouji is Ken's deceased older brother. Although he made only one appearance in one episode, and was only mentioned here and there throughout the series, he had a dramatic influence on the lives of the Chosen Children, particularly that of his younger brother, Ken. It had to do with the tumultuous and ultimately tragic relationship between him and Ken: both brothers originally got along quite well in the earliest years of their childhoods, as demonstrated by Osamu praising Ken's unique talent at blowing big bubbles, and Ken stating that he was proud of Osamu for being (at that time) the renowned boy genius of the family, the Grade-A student who excelled at everything.
However, as they grew older, their relationship was severely strained: Ken realized that he was often - if not always - overlooked and neglected by his parents completely in favor of Osamu, whose exceptional academic performances ensured that their parents were the objects of admiration and envy wherever they went. Naturally, it caused Ken to slowly but gradually become increasingly resentful and jealous of Osamu, to the extent where he started to wish that Osamu would disappear. Things took a turn for the worse after Osamu punished Ken for touching the Digivice which he thought was meant for him. As such, in a moment of thoughtless anger, Ken wished - with all of his heart and soul - that Osamu would just disappear.
Fate proved to have a twisted, cruel sense of humor by "granting" Ken's wish: Osamu was hit by a car and got killed.