This world is very new.

Giorno struggles to keep his face calm in front of this actual experienced hunter. He knew the easiest way to tell a lie was from one’s expression. “I’ve been training in hamon most of my life, plus skill is more important than age in this field, right?” He wills his face into a serene smile. “I’m Giorno Giovanna, nice to meet a fellow hunter.”

Giorno was the son of someone infected by a parasite. A hunter killed his father when he was four, and the Speedwagon Foundation took him in to be studied. Closer to a mutant than anything else they attempted to cure him, but he could only be cured to a certain extent. 

Unstable Worm here we go

Your local DIO here since being a vampire, carries a parasite inside his body working desperately hard to take control. Although, DIO’s body works against the parasite and instead gains power from it and prevents from escaping. The worm still grows inside of him both in size and in power which DIO then absorbs. They fit together like 2 peas in a pod but also they repeal like same sides of 2 magnets. Who knows how long it will be till both DIO and the parasite imploded from all the unstable energy they hold inside one body.