Did former President Moon Jae-in interfere in the 2018 Ulsan mayor election, helping the Democratic Party candidate? No, that's not true: There is no evidence this happened. The Seoul Central District Court did sentence, in November 2023, some officials affiliated with the Democratic Party in connection with suspected interference in the 2018 Ulsan mayoral election. Moon, though, was not a suspect in the case, and was not accused of any wrongdoing.
The claim originated from a video (archived here) published by @www.oung on TikTok, on December 2, 2023. It opened:
The culprit of the Ulsan mayor election fraud is Moon the Disaster.
(Translation from Korean to English by Lead Stories staff).
This is what the post looked like on TikTok at the time of writing:
(Source: TikTok screenshot taken on Thu Dec 28 05:19:30 2023 UTC)
The video claimed Moon rigged the Ulsan mayor election, citing a news report published by Hankook Ilbo on December 2, 2023 (archived here). But the article does not mention Moon being involved in the case. The Seoul Central District Court ruled on November 29, 2023, on allegations raised against Moon's presidential office, claiming that it helped the Democratic Party's Ulsan mayor candidate, Song Cheol-ho, in the 2018 local elections.
According to the prosecutor, (archived here) Moon's secretaries helped Song to be nominated as the party's candidate, consulted for his campaign platform, and pushed the local police to investigate his opponent Kim Ki-hyeon. The court found multiple people guilty, but Moon was not among them. The news article cited in the TikTok reports that the Seoul court sentenced (archived here) multiple officials, including the candidate himself, the local police director, and two presidential office secretaries. However, former President Moon was not a suspect in the case, and prosecutors did not accuse him of any wrongdoing.