Koji Minamoto is a main character in the Digimon anime series "Digimon Frontier". In this series, a group of chosen human children were given the ability to turn into digimon.

Koji was the child chosen to wield the Spirit of Light. Koji starts the series as the group loner - a kid who wanted friends, but never had the chance to make any because he had to change schools too many times. Koji receives Ophanimon's cell phone message while he was out buying flowers for his stepmother. He followed the instructions on the SMS, which led to a subway station where a Trailmon took him to the Digital World.

Koji travelled alone until he met Tommy and J.P. and had to save the two from a horde of attacking Pagumon. From then on, Koji showed up to help the other Digi Destined from time to time, and then eventually joins the group permanently. He often distances himself from the others, refusing to let anyone get too close to him. This was revealed to be because he moved a lot, and believes that no matter how close two people can get, something pulls them apart, so he stops trying to make friends and be, as he puts it, 'better prepared for it.' Originally, he is rather cold and rude towards the other DigiDestined, but eventually softens up as he becomes closer to them.

Koji has a rough relationship with his stepmother Satomi, whom he insists is : "Not my mom!" As such, he is distant from his father, who often tries pushing Koji into trying to get along better with her. Around halfway through the series, Koji realises that Satomi wasn't trying to take his real mother's place, but only wanted to be a part of his family. Upon returning to the real world, Koji decides to give her a second chance.

Koji also meets his twin brother, Kouichi Kimura, for the first time in the Digital World. Koji's parents had split up when they were young, and his mother had moved out with Kouichi Kimura and their grandmother. Koji's father remarried, told Koji that his mother had died, and never informed him of his twin brother. As such, Koji never knew he had a brother, let alone a twin.

Ironically, Koji was the last to find out that Kouichi, in the Digital World, was only spirit with a semi-physical form (in the real world, Kouichi fell down a flight of stairs and went into a coma). Bokomon overheard the conversation between Kouichi and Crusadermon, and was forced into telling the others (Takuya, Zoe, J.P, and Tommy) while Koji and Kouichi were out of hearing range.

After he returned home he accepted his stepmother and went with his brother to finally meet his mother whom his father had always told him was dead.
(Source: Wikipedia)