Diamond is Unbreakable - Chapter 23 
Koichi Hirose (Echoes), Part 5 (広瀬康一(エコーズ) その⑤ Hirose Kōichi (Ekōzu) Sono 5), originally A Deadly Sense of Guilt (死に至る罪悪感 Shi ni Itaru Zaiaku-kan) in the WSJ release, is the twenty-third chapter of Diamond is Unbreakable and the two hundred eighty-eighth chapter of the JoJo's Bizarre Adventure manga.
Tamami is being overwhelmed by the sounds and he shouts at Koichi to stop the cacophony, only for Koichi to reply that he will stop Echoes only when his family is safe. Echoes then plants another onomatopoeia, aggravating Tamami's position. However, the thug refuses to back down and pulls out of knife from a cabinet nearby. He stabs himself and fakes being badly hurt, then throws the knife at Koichi who catches it. Koichi's mother and sister come back to the family room, having been attracted to the ruckus, and see Tamami agonizing and Koichi with a blood-stained knife in his hand.
The Lock multiplies in size with their guilt and Tamami declares his victory, since Koichi's family will kill themselves out of guilt with Tamami being the only one able to stop them. Koichi's mother cannot bear her guilt and takes out a knife, preparing to stab herself. Tamami orders Koichi one last time to stop the sound, but he answers that he won't stop, and emit another sound. He shouts "Believe me!" toward his mother, imprinting the sound on her with Echoes. The sounds make her realize that she has to believe her son, and her guilt disappears.
Tamami, shocked by Echoes' power, yields and begs Koichi to spare him when he turns his attention to him. On Koichi's orders, he frees his sister as well and clings to his leg, begging again for mercy, suddenly looking very small compared to Koichi. When Tamami swears to obey Koichi's orders, Koichi uses the situation to demand 500,000 yen in return but shrugs it as a joke, but Tamami isn't entirely convinced that Koichi wasn't being serious.
The next day, Josuke and Okuyasu see Tamami sucking up to Koichi and wonder what happened between them.