Izumisano and Sennan mayors propose merger study group; Hannan and Kumatori invited
Version 2: The news moved from unnamed-source reports of a possible merger to an on-the-record proposal by the two mayors on 5 October, which named Hannan and Kumatori as invited partners, set a launch target of early 2027 and drew a deferral from the neighbouring leaders.
In short
The mayors of Izumisano and Sennan in Osaka Prefecture proposed on 5 October that their cities set up a study group to examine a possible merger, at a meeting of a wider body covering three cities and one town in the Senshu area, and asked neighbouring Hannan and Kumatori to take part. The body would be an arbitrary council rather than a legal conference, with a launch targeted as early as January 2027, and the cities cite population decline and a wish to strengthen Osaka’s “sub-capital” functions while seeking financial support. Hannan and Kumatori said they would take the proposal back to consider it.
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The mayors of Izumisano and Sennan proposed on 5 October that the two Osaka Prefecture cities set up a study group to examine a possible merger, at a meeting of a body discussing the future of the three cities and one town in southern Osaka’s Senshu area, Nikkei, TBS NEWS DIG and Mainichi Shimbun reported. Izumisano Mayor Chiyomatsu Daiko and Sennan Mayor Yamamoto Yuma made the proposal, the reports said. Nikkei said the group could launch as early as January 2027. [ 4 , 7 , 8 , 10 ]
Hannan and Kumatori were asked to take part and their leaders said they would take the proposal back to consider it, Mainichi reported. Yomiuri Shimbun reported that the planned body is an arbitrary council, not a legal conference under the Local Autonomy Act, that it would not treat a merger as a precondition, and that it would study a merger’s economic effects and impact on resident services, which Mainichi and TBS also reported. Mainichi quoted Chiyomatsu as saying it would be desirable to study a merger and draw a vision for the future, and Yamamoto as saying the merger should be an option rather than a precondition, with administrative efficiency and public facilities to be considered. [ 4 , 8 , 10 ]
The cities cite population decline and ageing public facilities and aim for sustainable local government and growth around Kansai International Airport, Mainichi reported. Sankei Shimbun, Livedoor News and Yahoo! News Japan reported they intend to argue that a merger would strengthen the functions of the “sub-capital” Osaka Prefecture seeks designation for, and to request financial support from the prefecture and the national government. [ 1 , 3 , 4 , 5 , 10 ]
Census figures for October 2025 differ slightly between outlets. Yomiuri, citing preliminary figures, put Izumisano at 100,329, Sennan at 56,136, Hannan at 47,657 and Kumatori at 42,511, all declining over the past decade. Mainichi gave the same four municipalities as 100,236, 56,107, 47,632 and 42,561. Sankei, Livedoor and Yahoo, citing census data, gave Izumisano 100,236 and Sennan 56,107, with Sennan down about 10% since 2015. [ 1 , 3 , 4 , 10 ]
The plan was first reported on 4 October, when Sankei, Livedoor and Yahoo said, citing people with knowledge of the matter, that the two cities had begun considering a merger and would launch a study group as early as January, inviting neighbouring municipalities. Those reports said the move comes about 20 years after the state-led Heisei-era mergers, and that municipalities in Ibaraki Prefecture are also exploring mergers. TBS noted that a new city in Osaka would be the first since that wave. [ 1 , 2 , 3 , 8 ]
A merger would require the municipalities concerned to pass council resolutions to set up a legal conference, draw up a basic plan, obtain a prefectural assembly resolution and receive a proclamation from the internal affairs minister, Sankei and Livedoor reported. [ 1 , 3 ]
Nippon TV News reported mixed views among Izumisano residents, with one saying a merger would be good in that the Sennan area would develop and another saying the cities should stay separate because each has its own strengths. Separately, Sankei reported that Osaka Prefecture will not conclude a cooperation agreement with Sakai over the sub-capital designation, quoting Governor Yoshimura as saying there is not much meaning in doing so at present. [ 5 , 12 ]
Why it matters
The two cities link the plan to Osaka Prefecture’s bid for “sub-capital” designation and say they would seek financial support from the prefecture and the national government, making the study as much about funding and status as about administration. The reports say the move comes about 20 years after the state-led Heisei-era mergers, when municipalities elsewhere, including in Ibaraki Prefecture, are again exploring consolidation, so the outcome may be watched by other local governments facing population decline. No decision on a merger has been made and no response from the prefecture is reported.
Key facts
- The mayors of Izumisano and Sennan proposed a study group on a possible merger at a meeting on 5 October of a body covering three cities and one town in the Senshu area of southern Osaka. [ 7 , 8 , 10 ]
- Neighbouring Hannan and Kumatori were asked to join; their leaders said they would take the proposal back to consider it. [ 4 , 10 ]
- The planned body is an arbitrary council, not a legal conference under the Local Autonomy Act, and does not treat a merger as a precondition. [ 4 , 8 , 10 ]
- The study group could be launched as early as January 2027, according to Nikkei, matching earlier reports of a launch next January. [ 1 , 2 , 3 , 7 , 10 ]
- The cities cite population decline and ageing public facilities, and aim to strengthen the functions of the “sub-capital” Osaka Prefecture seeks designation for while requesting financial support. [ 1 , 3 , 4 , 5 , 10 ]
- Census figures for October 2025 put Izumisano at about 100,000 and Sennan at about 56,000, with all four municipalities in the area on a declining trend; Yomiuri’s preliminary figures differ slightly from Mainichi’s. [ 4 , 10 ]
- A merger would require council resolutions to set up a legal conference, a basic plan, a prefectural assembly resolution and a proclamation by the internal affairs minister, Sankei and Livedoor reported. [ 1 , 3 ]
- TBS noted that a new city in Osaka would be the first since the Heisei-era wave of mergers. [ 8 ]
Confirmed by several sources
- Izumisano and Sennan have moved to examine a possible merger, first reported from people with knowledge of the matter and then proposed by their mayors. [ 1 , 2 , 3 , 4 , 5 , 7 , 8 , 10 ]
- Neighbouring Hannan and Kumatori were invited to take part in the study. [ 4 , 7 , 8 , 10 ]
- A study group is targeted to start around January. [ 1 , 2 , 3 , 7 , 10 ]
- The stated rationale includes population decline and difficulty maintaining services on their own. [ 1 , 3 , 4 , 5 , 10 ]
- The two cities link the plan to strengthening Osaka Prefecture’s “sub-capital” functions and to seeking financial support. [ 1 , 3 , 4 , 5 , 10 ]
- The proposal was made by the two mayors at the 5 October meeting of the wider Senshu area body. [ 7 , 8 , 10 ]
Still unclear
- The exact populations of the four municipalities as of October 2025. Yomiuri cites preliminary census figures (Izumisano 100,329; Sennan 56,136; Hannan 47,657; Kumatori 42,511) while Mainichi gives 100,236, 56,107, 47,632 and 42,561, and Sankei, Livedoor and Yahoo cite the Mainichi figures for the two cities.
- Whether Hannan and Kumatori will join the study group. Their leaders said only that they would take the proposal back to consider it, according to Mainichi, and no later decision is reported.
- Whether Osaka Prefecture or the national government will provide the financial support the cities intend to request. The documents report the intention to ask but no response from either government.
- The stance of Tajiri town, raised in a Nippon TV headline. Only the headline is available for that item; the document carries no article or summary text explaining the town’s position.
- Whether a merger will happen and when it would take effect. The planned body is described as a study group that does not treat a merger as a precondition, and no timetable beyond the study launch is reported.
- The exact membership and start date of the study group. Reports say it would be launched from January and that neighbouring municipalities would be invited, without a fixed date or confirmed participants.
What local media are saying
Timeline, local time
- Livedoor News reports that Izumisano and Sennan have begun considering a merger, citing people with knowledge of the matter. [ 1 ]
- Yahoo! News Japan carries the same report. [ 2 ]
- Sankei Shimbun carries the report, including background on the Heisei-era mergers and Ibaraki Prefecture. [ 3 ]
- Yomiuri Shimbun reports the two cities have decided to set up a council on the possibility of a merger and will propose it at the day’s meeting of the three-cities-one-town body. [ 4 ]
- Nippon TV News reports the two cities will launch a study group soon and will make the proposal at the afternoon meeting. [ 5 ]
- Nikkei reports the two cities announced at the day’s meeting a policy of setting up a merger study group, targeting launch as early as January 2027. [ 7 ]
- TBS NEWS DIG reports the two mayors proposed the merger plan at the meeting of the four municipalities. [ 8 ]
- Mainichi Shimbun reports the mayors’ proposal, the plan to start discussions in January and the call to Hannan and Kumatori. [ 10 ]
- Sankei Shimbun reports Osaka Prefecture will not conclude a cooperation agreement with Sakai in connection with the sub-capital designation. [ 12 ]