Koichi Hirose (Echoes), Part 1 (広瀬康一(エコーズ) その① Hirose Kōichi (Ekōzu) Sono 1), originally The Sinful Boy (罪深き少年 Tsumibukaki Shōnen) in the WSJ release, is the nineteenth chapter of Diamond is Unbreakable and the two hundred eighty-fourth chapter of the JoJo's Bizarre Adventure manga.
An anonymous caller calls Jotaro at his hotel, telling him that he is the one who stole the Bow and Arrow from Keicho. The caller presses Jotaro to leave Morioh, but once Jotaro starts questioning him, the phone is electrocuted and the call ended.
Meanwhile, Okuyasu has joined Josuke and Koichi's school while Koichi is riding gleefully on his new bike. The latter suddenly runs over a strange bag as he hears faint meows and sees a dark liquid oozing from the bag. Koichi understands that he has just run over a cat but tells himself that it wasn't his fault for someone left a bag with a cat in the middle of the road. A stranger called Tamami Kobayashi tells Koichi that he isn't guilty, even though his tone hints differently. Koichi tells Tamami that they must bury the cat and the latter replies that he will bury the cat if Koichi pays him, revealing that he was the cat's owner. Koichi begins to feel guilty when a lock latches onto him from thin air - Tamami's Stand, The Lock. Tamami tells Koichi that if he pays him, the guilt will disappear.