[ Information from Wikipedia - Spoilers may follow ]
Touma is a 14-year-old boy genius who graduated from the Stockholm Royal University of Science at the age of 12. His abilities are considered elite, even within DATS. He bases his operations on data and theoretical principles, and as such his personality clashes with Marcus's. His mother is Japanese and his father is a prominent Austrian aristocrat named Franz Norstein. He also has a younger sister, Relena, who suffers from a strange disease. Calm and shrewd, he is the exact opposite of Marcus and sees him as a rival. He has an elitist attitude but he gets emotional when thinking of his mother, who died years ago when he was young.
Touma's loyal partner is Gaomon, who always addresses him as "master" and gets angry easily when he thinks someone is not treating Touma with the proper respect. It has still yet to be revealed how the two actually met.
A great deal of Touma's background comes in episode 15, when MetalPhantomon manipulates his mind, feeding Touma nightmares from the past. We learn his mother died in a horrific accident in which she was killed by a speeding truck. However, the nightmare does not have the entire desired effect on Tohma, and he pulls through, allowing Gaomon to evolve to MachGaogamon.
In episode 28, he finally obtained the power to Digivolve his partner further, but his Digivice iC was not able to support the enhanced power of his Digisoul and shattered, with the same process happening to both Marcus's and Yoshino "Yoshi" Fujieda's digivice. In the following episode, he, along side his friends managed to repair their iC's and turn them into Digivice Bursts, allowing Gaomon to evolve to MirageGaogamon.
After the destruction of ElDoradimon, Touma was forced by his father to abandon his friends and side with DATS' greatest enemy Akihiro Kurata, who claimed to have the means to cure Relena. He even had to fight his former comrades, to the anger of Marcus, who accidentally invoked a dark Digi-Soul to fight him, with disastrous consequences. In the end Touma betrayed Kurata by destroying the device he was using to control Belphemon, and rejoined with his friends to confront him.
In episode 36 he also confronted his father that the only reason he went to study abroad was for him to become a physician, in order to find the cure for Relena's illness when any other doctor had failed before.
In episode 42, Tohma gets into an argument with his father and remembers how his grandmother hated him for not being born a "true" Norstein, being half-Japanese. While protecting the airplane where Relena was located, Touma fought against Crusadermon and unlocked MirageGaogamon's Burst Mode. After that, he rejoined the others and went to find Marcus back in the Digital World, partaking in all of the events leading up to the final battle.
After the defeat of Yggdrasil, Touma was forced to realize that the Digimon needed to go back to their own world, and spent one final evening with Gaomon. The next day, he and the others bid the Digimon farewell as they returned home, only to find out that Marcus had tagged along with them as well.
Five Years Later, Touma receives the Nobel Prize in Medicine at Stockholm City Hall, age 19, becoming the youngest person ever to win it, for finding a cure for Relena's illness.
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