Name: Ichijouji Osamu ( )
Meaning of name: reign (Osamu) first temple (Ichijouji)
Age: unknown, possibly 11 by the time he died
Appearances: Brief cameo in episode 21, more exposure in episodes 23 and 49
Voice Actress/Actor: Paku Romi, Kirby Morrow

What's known: Osamu is said to be the true genius in the family and was fawned upon by his parents to such an extent that Ken was completely neglected. Often stressed from the pressure that comes with being a child genius, he would occassionally and completely unintentionally lash out at his younger brother. This however does not indicate that he was abusive, for Ken's fondest memories were of them blowing bubbles out on the balcony and of Osamu explaining that Ken was far more gentle and kind than he was. Unfortunately, after one argument Ken wished that Osamu would die.

Not long afterwards, Osamu was hit by a car and killed.

The history of the Ichijouji brothers is relatively complex. When the digivice was sent to Ken, Osamu confiscated it and put it away with the warning that Ken was not to touch it. However, curiosity plagued the younger boy, and Ken sneaked it out and was transported to the Digital World. Once he returned, his brother discovered his betrayal of trust and snatched the device away. Ken did not enter that world again until after Osamu's death.

Ken constantly blamed himself for Osamu's death to the point where he attempted to make up for the loss and attempt to appease his parents by taking Osamu's place, and continued to do so until his vision during episode 49.