The gangsters are two trios of minor villains from Higurashi no Naku Koro ni Kira, the light-hearted and comedic OAV fourth season of Higurashi no Naku Koro ni. They appear in Musubienishi-hen.
The first trio of gangsters was seen hanging out at Angel Mort where Keiichi Maebara had been invited to its dessert feast by Shion Sonozaki, who had disguised herself as Mion during her inviting of him earlier. The gangsters fell in love with Shion, whom they thought was Mion and tried to steal her, but Keiichi saved her and stood up to them, scaring them into running away from Angel Mort as fast as they could.
Later, another trio of gangsters, this time bikers, also met Keiichi and Shion at a sidewalk. The bikers also fell in love with Shion and tried to steal her as well, but Keiichi was quick to get in their way and stand up to them as well to protect her, which reminded Shion of Satoshi Hojo protecting her. The bikers managed to knock Keiichi down however, and were about to steal Shion, but luckily, her bodyguard, Kasai Tatsuyoshi, came along and gave the bikers an angry look in his eyes. Kasai's angry look scared the bikers and chased them away as well.
The bikers previously appeared in Higurashi Kai's Minagoroshi-hen, where they assaulted Rika only to be stopped by Kasai.