Tsu Kim is an agent with the NIS.
That acronym stands for the National Intelligence Service, the key espionage organization of the South Korean government. When we first meet her in her solo adventure (so far), she has "recently finished her training and passed with high distinction" and was anticipating being assigned her first mission which she expected would take her away from her home and likely country for some time.
Kim's immediate supervisor was a man named Park with whom she has an interesting relationship in that some days he can be very pleasant to be around while others, more common, he can be a bear. It will be that connection which will affect her career quite a bit later on.
It will be from Park that we learned Kin "aced" her training, scoring the "best of all new recruits on the psychometric testing" and "held out longest in several of the endurance tests". What this showed him and what we will witness in her actions during her missions is that Kim really hates to lose and the idea of quitting just never enters her mind. This tenacity will push her through some pretty nasty situations.
That determinedness will also see her career take a major veer after that initial mission. Her unwillingness to walk away from a job unfinished, leaving a young girl in considerable peril, despite being ordered by the top brass, will get her officially fired from the NIS. In truth, she will be assigned a partner and start work as an unofficial operative doing off-book work for Park.
Kim is the daughter of a Japanese woman and a Korean father. She was born in Japan but moved to South Korea when she was young. While she wanted for some time to work for the NIS, she still feels a tad torn between her birth country and her adopted one. When asked where she was from, she wistfully replied, "I wish I could say I was from somewhere, but I don't really feel like I am."
Tsu Kim muses on the difference in beating intel out of someone or seducing it: "An important part of her job was getting information from people. Hurting people was effective, but it was also bad for the soul. Charming people wasn't easygoing on the soul either, but at least it varied things up a little."