Asatō Line

The line is the surviving fragment of a much larger unbuilt scheme. Under the amended Railway Construction Act it was planned as part of the Asa Line (阿佐線), a route intended to link Mugi in Tokushima with Gomen in Kōchi by way of the Cape Muroto coast. The northern Tokushima end, from Mugi to Kaifu, opened as Japanese National Railways' Mugi Line on 1 October 1973, and the western Kōchi end, from Nahari to Gomen, eventually opened as the Tosa Kuroshio Railway's Asa Line on 1 July 2002. The central Kannoura–Nahari section was never built and remains a missing link served only by road, leaving the Asatō Line as the eastern stub of the original plan.

Construction of the Kaifu–Kannoura section was frozen in 1980 under the JNR Reconstruction Act, even though the works were by then almost complete. Rather than abandon the nearly finished line, Tokushima Prefecture and other local bodies decided in 1988 to take it over through a third-sector company, established the Asa Coast Railway Company, and resumed construction on 29 March 1989. When the line finally opened it became the first private and the first third-sector railway in Tokushima Prefecture since 1944, the year the Hashikura mountain railway had closed and left the prefecture's railways entirely in JNR (later JR Shikoku) hands.

The Kaifu–Kannoura section opened on 26 March 1992, a goal local newspapers described as the fulfilment of a seventy-year wish. From the start the line was worked by one-person crews, and JR Shikoku limited expresses ran through onto it: the "Uzushio" reached Kannoura from the opening, the "Tsurugi" from 1998, and the "Muroto" from 1999. Together with JR Shikoku's Mugi Line the route was given the nickname "Awa Muroto Seaside Line" from 1 July 2002, and station numbering (line symbol AK) was introduced in 2006. Over the following years through-running with the Mugi Line was repeatedly cut back and partly restored before the last limited-express working, the "Tsurugi," was withdrawn in 2011.

Even so the Asatō Line carried very few passengers — its transport density was only a few hundred people per day — and its long-term survival was in doubt. From 2011 the prefecture and the railway studied the dual-mode vehicle, a road-and-rail vehicle seen as a cheaper alternative to conventional diesel railcars on lightly used lines, and ran demonstration tests. In February 2016 Tokushima Prefecture announced its intention to put DMVs into commercial service within ten years, and in February 2017 it formally decided to introduce them by 2020. The plan envisaged vehicles that would run as buses on ordinary roads, switch to rail at changeover points, traverse the existing line, and then return to the road to reach destinations without any track.

Preparing for DMV operation required physically reshaping the line. In summer 2019 the Asatō Line was severed from the Mugi Line so that mode-changeover facilities could be built, and the three DMV vehicles — extensively modified Toyota Coaster minibuses classed as the DMV93 type — were completed and unveiled during 2019. On 1 November 2020 the short Awa-Kainan–Kaifu section of the Mugi Line was transferred from JR Shikoku and absorbed into the Asatō Line, and conventional diesel railcar operation (the ASA-100 and ASA-300 series) ended on 30 November 2020. Bus substitution then covered the route from 1 December 2020 while the changeover facilities at Awa-Kainan and Kannoura were completed.

The switch to DMV operation, originally aimed at 2020, slipped repeatedly — held up by the COVID-19 pandemic and by a mid-2021 finding that a front-axle support part needed strengthening — before regular service finally began on 25 December 2021, hailed in the Japanese press as the world's first commercial DMV operation. Trains now start as buses at the Awakainan Bunkamura stop, enter the rails at Awa-Kainan, run south to Kannoura, and continue by road to Michinoeki Shishikui Onsen, with one weekend-and-holiday round trip extended along the old Asa Line alignment toward Cape Muroto. With the change, the line's railway terminals at Awa-Kainan and Kannoura became signal stations and road-interchange points, so that only Kaifu and Shishikui remain railway stations under the Railway Business Act; the small DMV fleet has since required repeated timetable reductions and safety-inspection suspensions, in 2023 and 2024, underscoring how marginal the operation remains.

• 19731 October: the Mugi–Kaifu section opens as Japanese National Railways' Mugi Line, the Tokushima-side portion of the planned Asa Line.
• 1980Construction of the Kaifu–Kannoura section is frozen under the JNR Reconstruction Act, although the works are by then nearly complete.
• 1988Tokushima Prefecture and other local bodies decide to take over the nearly finished line through a third-sector company and found the Asa Coast Railway Company.
• 198929 March: construction of the Kaifu–Kannoura section resumes under the Asa Coast Railway Company.
• 199226 March: the Kaifu–Kannoura section opens as the Asatō Line; one-person operation begins and the JR Shikoku 'Uzushio' limited express starts running through to Kannoura.
• 199814 March: the 'Tsurugi' limited express begins running onto the line.
• 199913 March: the 'Muroto' limited express begins running onto the line, replacing the through 'Uzushio'.
• 20021 July: together with the JR Shikoku Mugi Line, the route is given the nickname 'Awa Muroto Seaside Line'; the western Nahari–Gomen part of the old Asa Line opens the same day as the Tosa Kuroshio Railway's Asa Line.
• 20061 March: station numbering (line symbol AK) is introduced at all stations.
• 201112 March: the 'Tsurugi' limited express through service is withdrawn, ending limited-express running onto the line.
• 2016February: Tokushima Prefecture announces its intention to introduce dual-mode vehicles (DMV) into commercial service within ten years.
• 2017February: introduction of DMVs by 2020 is formally decided.
• 2019In summer the Asatō Line is severed from the Mugi Line to allow DMV changeover facilities to be built; the three DMV93-type vehicles are completed and unveiled during the year (all three shown on 5 October).
• 20201 November: the Mugi Line's Awa-Kainan–Kaifu section is transferred from JR Shikoku and incorporated into the Asatō Line; conventional diesel railcar operation (ASA-100/ASA-300 series) ends on 30 November and bus substitution begins on 1 December.
• 202125 December: regular DMV service begins between Awa-Kainan and Kannoura (with road sections to Michinoeki Shishikui Onsen and toward Cape Muroto), reported as the world's first commercial DMV operation; the railway terminals become signal stations.
• 202311 March: a timetable revision reduces weekday DMV trips (to eight round trips on Tuesdays and Wednesdays) and weekend/holiday trips, reflecting the small fleet.
• 202416 March: a further timetable revision standardises weekday operation at eight round trips; on 3 October all three DMVs are suspended for detailed inspection after a minor defect is found, with service resuming on 12 October.