Not very accurate, perhaps, but this is just my 2 cents on what I think Giratina is
He's the embodiment of chaos. To be exact, a naturally-happening chaos (like natural disasters, viruses, basically things that aren't made by humans.), not those that happens because of humans (e.g: terrorisms, bombing, etc.). Keep in mind how Giratina's home is the Distortion World - a place that probably represents the parallels and chaos happening in the human world. The one that I think represents man-made chaos is Zygarde - Which i'll explain later on maybe because I don't want to make this answer seem too long.
Well, might seem a little dumb but anyways, I still want to share my 2 cents.