Marty is the reason that the events of Faded Blue are happening.
Marty was the one who stopped Greg from achieving fame by taking most of his money and taking him to places like Beach City, where there were few people to watch him and he wasn't advertised properly. By bringing him to Beach City, he met Rose and chose love over music, as he wasn't successful anyway. In Faded Blue, by not meeting Marty, he achieved fame as Marty wasn't hindering him, and toured to Korea, where he met Blue Diamond and fell in love. Additionally, the Cool Kids consist of Buck, Jenny, and Ronaldo - completely missing out Sour Cream, who possibly doesn't exist now, because Marty never went to Beach City with Greg, and therefore never met Vidalia. Thanks, Marty.