So-Sul Woo

Jang So-Sul / Sun-Woo So-Sul is the former head of the Sun-Woo Clan, like her father. So-Sul is small and has a weak frame due to her unique body condition which makes her seem younger than she really is (a fact that greatly annoys her as Shi-Woon treats her like a little child). In the beginning, she cannot talk due to her unique condition; whenever she does, she is come over with a coughing seizure. But due to Shi-Woon Yi administrating his blood to her as a remedy and then massaging her body, she can now talk more due the vast amount of ki in Shi-Woon's blood. Despite her appearance, and even her age (15 Years Old), she is incredibly mature, a trait that is shown in her almost aristocratic style of speech and her self-denial of a teenage lifestyle. She appears to be calm even when there is danger although it was revealed that she was afraid since she saw the same things in nightmares and was scared. She seems to be shy and the type that does not show her true desires and always acts as though she is forced to things that she actually wants to do, like when she played with Shi-Woon in the sand making castles.

(Source: The Breaker Wiki)