The story is set in the city of Kuopio, in Finland, a decadent China-esque nation in Scandinavia characterized by social inequalities, rampant crime, religious conflicts between the Muslim Uyghurs and the Buddhist majority, and powerful Triad mafias that hold the entire country in their grasp. The governor of Kuopio, Kuusinen Vilho, is a corrupt man connected to the powerful Triad "Reqing" (counterpart to Passione, as Reqing means "passion")
The protagonist is Zhou Zhongshan (Zh in Chinese is pronounced as J, so he's pronounced "Jo Jongshan"), nicknamed "Insomnium" because he suffers from insomnia due to a past trauma (he's the SBR counterpart to Giorno Giovanna), a 24-year-old mercenary who accepts missions even from the Triads. He loves riding his Honda motorcycle and playing Avicii songs with a traditional Finnish Sheng mouth organ. He's named his Stand Avicii ("Naraka" in the censored version).
Insomnium receives a mission from a certain Woon Zemin: he has to guard his adoptive daughter, a young girl named Woon Touko who studies at Guangdong High School (SBR counterpart to Trish, her real name is Mao Touko, and she's the daughter of Reqing boss Mao "Perkele" Untamo, counterpart of Diavolo). That Zemin's letter opens with "If you receive this letter, it means that I've already been murdered". Insomnium waits for the girl, and sees her attacked by Wang Mahmoud, a hitman from the Muslim terrorists "Allah's Guard".
As he saves Touko, he's dragged into a conflict for the fate of the city, as both men from Reqing and Allah's Guard are looking for her. He's attacked by dozens of men from Reqing and guided to safety by Yasuho Hirose, coming from Japan to look for Touko herself (unlike Koichi in the original series, Yasuho is a permanent member of the party). Having left Josuke in Japan with a son, Masanosuke, Yasuho has been sent by the Japanese government to investigate on the Triad boss Perkele (who also controls some Yakuza in Japan) and arrest him. Perkele's name (Mao Untamo) is not known to the public, and, unlike Diavolo, Insomnium actually meets Mao Untamo disguised as a civilian early on, as they frequently play hanafuda in the Kuopio casino, and Zhongshan sees Untamo as a hero and the closest thing he has to a father due to him having saved Zhongshan's life when he was dying as a child (naturally, Zhongshan doesn't know Untamo is Perkele, but Untamo knows Zhongshan is Insomnium)
NOTE: all character names are in Chinese name order (last and then first) to give a less European and more Chinese feel to the city of Kuopio, since Finns aren't Indo-European but related to Mongols and Uyghurs from China.