The crystal is a mysterious artifact which is the source of Han Yu-Hwa's powers. The crystal has its own will thus making it quite different from power orbs of dead Anothers. Also, Sa-Ryun acknowledges it as a high purity crystal when he first sensed its presence.
15 years prior to the current storyline i.e. at the age of 6 years, Han Yu-Hwa found a crystal in some mountain ruins. The crystal emitted a radiant glow for which it was mistaken as a gem by Yu-Hwa. When he tried to take it, the crystal emitted a large glow and merged with Yu-Hwa. It is unknown how it arrived into those mountain ruins, but a skeleton was seen besides the crystal, and it's likely they are related to each other.
At the age of 21, the crystal reacts within Han Yu-Hwa for the very first time. When he takes the blow from the running truck, his life is jeopardized and a crack appears on the crystal. It is then that Sa-Ryun senses its presence which means the crystal power was emitted.
After returning home from hospital, Yu-Hwa is attacked by the same Another whom he fought in the hospital. A fatal blow from the Another puts Yu-Hwa's life to jeopardy once more and the crack of the crystal turns into a glaring glow. For a second time, it emits power and Yu-Hwa not only recovers but his body reacts and he is able to fight the Another. However he collapses soon.
At the third time, the crystal is awakened when Yu-Hwa is rendered severely injured once more by the same Another in an attempt to save Detective Park. He pleas the voice within to save him and the crystal responds. Yu-Hwa gains power and his right hand transforms with energy of same color as the crystal emitting from it. Both the Another and Sa-Ryun sense it.