To install you need Openiv for the model.
You also need it for Giorno's textures (In case you want to change them).

Note:
This is my first time doing mods like this and the Requiem model has a bug in the waist accessory but don't worry it's actually the power of Requiem.
Just kidding I forgot to render that part well and also Requiem had some more accessories.
Well enjoy the mod and help Giorno fulfill his dream.

Note 2: At first you may get an error, just insist two more times and if the same error appears, which is w78 something, 
just be patient and wait a bit and the game will open.

Note 3: Use a Mod Menu I recommend Zolikas trainer.

Note 4: To use Giorno's textures you must install the following Mod

https://www.gtainside.com/en/gta4/skins/153758-giorno-giovanna/