Note: I'm intentionally leaving out a lot of specifics here, because I'd prefer that they're discovered through game play.
Jun was selected by an unknown Chinese ministry at 5 years of age because he was something of a savant with computers and science. Instead of attending a normal high school, the Chinese organization took him and trained him especially to be what he is. His entire family was also taken into shelter. The organization took special pains to cover his identity, and all records in China would indicate that he lived a relatively normal life. E.g. he has normal high school transcripts, birth records, place of residence, etc on record.
When he completed his training at 18, they moved him to [insert university name here] in [insert American city here] and continued to give him a cover story. They gave him employment at U.S. Robotics, with a full college scholarship to pursue scientific studies abroad.
Before attending college, he was "employed" by U.S. Robotics as part of their agreement. In reality, during this time, he was undergoing grueling physical surgery to install top-secret cybernetics. Even today, he undergoes occasional maintenance there as well as software and hardware upgrades. U.S. Robotics also gives him the resources to develop his own gadgets. (This is where he gets his "gear" from.)
His immediate family (mother, father and brother) was brought with him as part of the company's "incentive package." He is now attending school and awaiting orders from his source, Yun Kim, who resides in China.