Jazz Fenton
Jazz is Danny's big sis. She is the smartest girl in her school, and an extremely mature teenager. Usually the one who looks after Danny, and probably the only one in her family that has a clue of what is going on. At the beginning of the series Jazz thinks ghost are a waste of time. However when she discovers Danny's secret without him knowing, Jazz is there to help Danny each time she can. Mostly from trying to keep his ghost powers a secret and giving excuses to others about Danny's weird disappearances to finally enjoying the family business.*Spoiler* At the end of The ultimate enemy Danny encourages Jazz to tell him, that she knows about his powers. Later on in the series, we see Jazz like a more active help to Danny, fighting against ghost and even against Vlad.