Minami-Rias Line

The corridor began as a Japanese National Railways (JNR) project to serve the isolated fishing communities of the southern Sanriku coast. JNR opened the Sakari Line from Sakari to Ayori, a distance of 9.1 km, on 1 March 1970, and extended it from Ayori to Yoshihama, a further 12.5 km, on 1 July 1973. The remaining stretch on to Kamaishi was still under construction, leaving the line short of its intended northern terminus for years.

Like other lightly used local lines, the Sakari Line was slated for closure as JNR's finances deteriorated in the early 1980s. Rather than abandon it, Iwate Prefecture and the municipalities along the coast established the Sanriku Railway in 1981 as the country's first 'third-sector' (joint public-private) railway company. On 1 April 1984 the company opened the whole Sakari–Kamaishi route as the Minami-Rias Line: the former JNR Sakari Line section was transferred to Santetsu and the newly built Yoshihama–Kamaishi section, 15.0 km long, opened at last, completing the line. The same day, the company also opened its northern Kita-Rias Line, and the two together formed the original Sanriku Railway network.

For a quarter of a century the line carried local passengers along a remote and scenic coast. That settled existence was shattered on 11 March 2011, when the Great East Japan Earthquake and the tsunami it generated struck the Sanriku coast. The entire line was suspended; across Sanriku Railway's two lines damage was recorded at roughly 300 locations, including station buildings and bridges, and the tsunami washed away some 5.8 km of track.

Reconstruction of the South Rias Line took longer than on the northern line, and service returned in two stages. On 3 April 2013 the Sakari–Yoshihama section, 21.6 km, reopened, restoring trains over the southern half of the line. Full restoration came on 5 April 2014, when the worst-damaged Yoshihama–Kamaishi section, 15.0 km, returned to service and the Minami-Rias Line was once again running end to end — part of the wider restoration of the whole Sanriku Railway network completed that April.

The line's final transformation came in 2019. The parallel JR East Yamada Line, which carried the Kamaishi–Miyako section between Santetsu's two lines and had opened in stages in the 1930s as part of the Railway Ministry's Yamada Line, had also been severed by the tsunami. Rather than restore that section itself, JR East rebuilt it and handed it to Sanriku Railway. On 23 March 2019 that transfer took effect, linking the Minami-Rias Line at Kamaishi with the Kita-Rias Line at Miyako to form a single continuous Rias Line of 163.0 km and 41 stations, running from Sakari in Ōfunato to Kuji.

The South Rias name endures as the Sakari–Kamaishi administrative section of that unified line, 36.6 km of the 163.0-kilometre whole, and it is the name carried on this map. Diesel railcars still thread the rugged, ria-indented coast that gives the line its name, and the route remains a lifeline for the coastal communities of southern Iwate and an enduring emblem of the Sanriku region's recovery from the 2011 disaster.

• 19701 March: JNR opens the Sakari Line from Sakari to Ayori (9.1 km), the first part of what becomes the Minami-Rias Line.
• 19731 July: the JNR Sakari Line is extended from Ayori to Yoshihama (12.5 km); the section on to Kamaishi is still under construction.
• 1981Iwate Prefecture and coastal municipalities establish the Sanriku Railway, Japan's first third-sector railway company, to take over the JNR lines slated for closure.
• 19841 April: Sanriku Railway opens the whole Sakari–Kamaishi route (36.6 km) as the Minami-Rias Line — the former JNR Sakari Line is transferred and the new Yoshihama–Kamaishi section (15.0 km) opens, completing the line; the Kita-Rias Line opens the same day.
• 201111 March: the Great East Japan Earthquake and tsunami suspend the entire line; across Santetsu's two lines damage occurs at ~300 locations and about 5.8 km of track is washed away.
• 20133 April: the Sakari–Yoshihama section (21.6 km) reopens, restoring trains over the southern half of the line.
• 20145 April: the worst-damaged Yoshihama–Kamaishi section (15.0 km) reopens, fully restoring the Minami-Rias Line as part of the wider restoration of the whole Sanriku Railway network completed that April.
• 201923 March: the rebuilt JR East Yamada Line section from Kamaishi to Miyako is reopened and transferred to Sanriku Railway, joining the Minami-Rias Line at Kamaishi with the Kita-Rias Line at Miyako to form the single through Rias Line.
• 2019The unified Rias Line runs 163.0 km from Sakari (Ōfunato) to Kuji with 41 stations; the Minami-Rias Line endures as its Sakari–Kamaishi administrative section (36.6 km).
• 2019Wikidata records the Minami-Rias Line as a railway line that ended on 23 March 2019, 36.6 km long, operated by Sanriku Railway — confirming its absorption into the Rias Line.