An Jing was very aware that it was because Nian Quan was quite young, having received his own legacy, he could not keep his feelings to himself, was unable to stay calm, and thus wanted to repay something right away.
It made sense, too, given Nian Quan's inherent talents and personality, after years of silence and although he could endure, he must have been feeling extremely stifled.
After obtaining the Heavenly River Life and Death Sword, he had certainly shown off his skills and had his moment of glory, and now he had even become the team captain at the school, able to directly communicate with the Principal, presenting himself as a campus leader—how could he not feel grateful to An Jing, who had changed his fate?
Not to mention a Great Void Magical Instrument, even if An Jing asked him for something even more precious or all of his possessions, Nian Quan would have undoubtedly agreed without hesitation.