Taiwan's opposition is lining up behind a single challenger in Tainan, a Democratic Progressive Party stronghold, setting up a rare competitive race in the city.

• Hsieh Lung-chieh has formally registered to run for Tainan mayor and says the blue-white opposition alliance in the city is fully settled.
• He is pledging to serve only one term and not seek re-election, framing that as proof he can push reforms without political baggage.
• His pitch rests on corruption complaints built up over eight years and on the argument that 33 years of one-party rule in Tainan is enough.
• DPP legislator Chen Ting-fei is running for the same seat and registered alongside the party's city council candidates under a unity banner.
• A failed opposition deal in Zhubei raises questions about whether the alliance holds elsewhere, though Tainan is being kept separate from that.

Outlook: Expect the race to turn into a straight test of whether opposition cooperation can dent the DPP's oldest power base, with local council seats as the real battleground.