As a young girl, Crystal (Kris for short) went into the mountains to train; presumably to catch Pokemon, and it is strongly implied that her mother pushed her to do it. A misstep caused her to fall from a ledge, and though her Pokemon rescued her, she still broke her arms, and as such, she had to rely on her legs; learning to kick Pokeballs at their targets. The extra power facilitated by her honed skills proved extremely effective, and she retained the method even after healing.
Sometime later, Crystal began volunteering at a school, but lack of funding threatened to bankrupt the institution. Fortunately, Professor Oak was visiting Johto, seeking to hire an assistant to help him document the region's Pokemon, and so Crystal accepted, utilizing her capture skills in to earn money and save the school. Subsequently, she continued capturing out of passion.
Crystal began feeling very proud of her skills, and though often they were useful to others, she developed a somewhat unhealthy fixation on testing her skills. This became detrimental when she attempted to capture Suicune, the legendary water Pokemon. Despite Crystal's good plan, the creature escaped, and her obsession turned into a disillusioned incompetency. At the behest of her mother, she returned to the mountains and tied her arms in a cast, recreating the circumstances under which she trained herself to kick balls, and upon being attacked by a hostile Pokemon, regained her will and her skills; capturing it to save herself. From then on, however, her life would turn away from simply capturing Pokemon.
Clash of Legends
Having met Lt. Surge, Bill, and Yellow in her adventures, Crystal joined their quest to find and rescue Gold and Silver, and help battle the new leader of Team Rocket. Upon meeting the missing boys, the group was confronted by the tornado-powered legendary bird, Lugia. Utilizing teamwork in which Gold disabled the creature's ability to attack, Kris again kicked a ball at Lugia. It seemed the battle was won, but the celebration was short-lived, as when Kris recovered the ball, she found it empty. Though the party didn't know it at the time, the leader of Team Rocket had flown in to snag Lugia himself, and had frightening ambitions for it.
The group had heard, however, that the leader was also a Gym Leader in Johto, so they decided to attend a tournament of Gym Leaders to find him out. It turned out that he had thought ahead, however and trapped them in the control room, while also trapping the other Gym Leaders in a moving train. Gold and Crystal eventually escaped, while the Gym Leaders were rescued by Red, Bruno, and Koga, but the leader of Team Rocket, now revealed as Bryce, the Ice Master, had succeeded in forcing a Pokeball crafter to build a "Time Ball." Here, he announced his plans; he aimed to capture the legendary Celebi with the ball, and rushed to its sanctuary. Yet all of Pokedex holders from Kanto and Johto had gathered to stop him, joined by other legendaries including Suicune, and its allies, Entei and Raikou. Suicune, remembering her determination, chose Kris as his human ally, and the heroes charged after Bryce; pursuing him through time to the time when he was a young man. There, it was revealed that Bryce's intentions were fundamentally good, as he just wanted to save his pet Lapras that he lost in his youth. In the final confrontation, he abandoned his vendetta on the world. The crisis over, the three legendary beasts returned to their slumber, and Kris and Suicune parted ways now seeing each other as equals and friends. She now remains good friends with Gold and Silver.
Crystal is indisputably the master of her craft, having developed a perfect set of skills utilized in capturing Pokemon. She is exceptionally athletic, and the technique, aim, speed, and strength of her kicks strongly suggest a history of martial arts training, although she has yet to be shown fighting directly. However, she also has quite a procedural intellect on her side, as she is able to form complex plans to capture tougher Pokemon.
The downside to her tenacious approach is that she can come off as aloof to her peers. Single-minded pursuit of goals has backfired on her, and she seems to have little patience for un-serious chatting. This places her at odds with Gold, who is happy, fun-loving, and a bit naive, although they remain allies.