What do you love the most about Killua???

My exam was HORRIBLE, I need a refreshment, tell me what do you love the most about Killua ? I love this boy so much , I especially love his boyish and playful attitude, he's fun to watch.

His character arc is beautiful too , it's so inspiring and refreshing, most of shounen deutagonists tend to develop a negative outcome because of their trauma, but Killua did the opposite, he's amazing.