Fugo is a member of Buccellati’s gang and is known to lose his patience and explode with anger. He is also the main character of the spin-off novel Hajishirazu no Purple Haze: JoJo no Kimyou na Bouken yori.
He uses his Purple Haze to help retrieve the key and after safely escort Trish to the boss. However, he was unsure about following Bruno in betraying the boss, so he decided dropped out of the gang. Aside from the epilogue (which is set in the past), he is not seen again in the manga.
In Volume 10, Araki explains that the plot originally had Fugo working as a spy for Diavolo that Giorno would have eventually been forced to kill. Having gone through grim feelings at the time, Araki couldn’t handle the thought of betrayal of a dear friend and felt that the readers would have been disappointed had he followed through, thus the goodbye scene at the quay of San Giorgio Maggiore happened
Purple Haze’s hands have packages of a “delay virus”. Once released, everything around it will die in 30 seconds. It does not matter if it is an ally or enemy, for there is no controlling the virus.