Killua with no affiliation from a known family was a famous yet mysterious immortal in the Cloud Continent. Not just because of his obvious talent with a sword, but also because, despite being immortal, he only uses martial arts rather than mystical ones.
Martial Techniques are becoming less formed in Immortal Heaven. As Mystical Arts were becoming more popular with others, they just had a simpler and more powerful impact on the enemies.
Being untalented in mystical arts or limited to martial arts denotes weakness in Immortal Heaven. Immortals discriminate against those who were limited to martial arts because of how the two vastly differ.
When a mystical art form is used, an unexplainable phenomenon can occur. A mystical art attack could be otherworldly and unique in its method of killing.
