As a child, he was raised to be a devout Renraku man by his wageslave father, living in Kobe. He ran slightly afoul of expectations as a teenager when he and some friends highjacked a Shiawase truck containing cutting-edge prototypes and were caught, damaging the reputation of both Renraku and his father. Despite this, he was able to enter Kyouto University, where he studied military tactics, political science, and economics. At this time he had a friendship with young woman from Kyouto that nearly blossomed into a romantic relationship, and he often thought of her fondly years later.
He was able to join the ranks of the elite Red Samurai, Renraku's special forces division, where by all accounts he served as a capable soldier for many years. However, he was forced to flee when he contracted the ghoul plague, due to Japan's stringent laws on mutation. Hunted by his former comrades, he fled to Shanghai, not wishing to go far as he still hoped to find a cure and felt that staying nearby felt less like leaving. At this time, he took the name of Gaichuu, meaning "annoying insect." He quickly found that the Renraku presence in Shanghai was too strong, but managed to take refuge in Hong Kong, where he became a shadowrunner. Though his condition had blinded him, he retained his Red Samurai skills, and was even able to put his new ghoul abilities to good use.
At some point, he was contacted by the Whampoan Elders to assassinate one of their own who had been causing a problem. However, the Elder who had fixed the job refused to pay, and, to protect his reputation, Gaichuu began systematically murdering the remaining Elders in retaliation. Eventually, a team of shadowrunners in the employ of Kindly Cheng was contracted to hunt down and kill Gaichuu, though they ultimately learned the truth and saw that justice was meted out.
After this, Gaichuu may have become a member of this team of shadowrunners. If so, then they likely assisted him in one final armed confrontation with his old squad, which they summarily wiped out. Gaichuu intended to turn his old CO into a ghoul, that he might be forced to endure the same suffering and loss of honour that Gaichuu himself had, but may have been persuaded to deal him a merciful death in stead.