Tosa Kuroshio Railway Asa Line

The line is one part of a far larger plan. Under Table No. 107 of the revised Railway Construction Act of 1922, the state designated a predetermined line running "from Gomen in Kōchi Prefecture via Aki and Hiwasa in Tokushima Prefecture to the vicinity of Furushō", under the "Shikoku Loop Railway" concept. The Tokushima end of this corridor between Muki, Hiwasa and Furushō opened between 1936 and 1942 and today forms part of JR Shikoku's Mugi Line. The remaining stretch, planned to connect Muki with Gomen at roughly 113 kilometres, became the Japanese National Railways construction line known as the Asa Line.

The Asa Line advanced slowly through the bureaucratic stages of railway planning: a predetermined line in 1922, a survey line in 1957, and a construction line in 1959, before being placed under the Japan Railway Construction Public Corporation as a works line in 1964. Construction began at the ends that connected to existing track. On the Tokushima side, work started from Muki, and on 1 October 1973 the Muki–Kaifu section (11.6 km) opened as part of the JNR Mugi Line. On the Kōchi side — the segment known as the Asa-sai (West Asa) Line — groundbreaking for the Aki–Tano stretch took place in 1965 under the loop-railway concept, and viaduct work between Gomen and Aki followed from April 1974.

Between Gomenmachi and Aki, the Tosa Electric Railway had run its Aki Line, opened throughout in 1930. From the 1970s its deficits grew markedly as freight traffic ended and passenger revenue fell, and it was abolished at the end of March 1974. Following the example of the Kōjaku Railway, the closure was meant to clear those deficits through the sale of the line's land, in the name of promoting construction of the JNR Asa Line.

The project then collapsed. In December 1981, under the Special Measures Act for the Promotion of JNR Management Reconstruction, construction of the Asa-sai Line was frozen; work on the Tokushima side had already been halted on 27 December 1980, when the act was promulgated and took effect. At the freeze, 18.9 km of the Asa-sai Line, about 44 per cent of its full length, had been completed, and its half-built viaducts and embankments were left standing for many years, a sight that earned the names Tosa's "Great Wall" and Tosa's "Tower of Babel". The central section between Kōnoura, Muroto and Nahari remains an uncompleted line to this day, with the gap covered by local buses.

Rescue came through the third-sector model. In February 1986 Kōchi Prefecture and the heads of the municipalities along the Asa and Sukumo lines agreed at a joint meeting to set up a single third-sector company for the two lines. On 8 May 1986 the Tosa Kuroshio Railway was founded, led by Kōchi Prefecture, to take over construction of both abandoned lines. The new company obtained its Class-1 railway licence for the Gomen–Nahari section in January 1988, and construction resumed in March of that year. The firm, however, concentrated at first on building the Sukumo Line and on sustaining the Nakamura Line, so the Asa-sai Line was given lower priority. On the Tokushima side, the separate Asa Kaigan Railway opened the Kaifu–Kōnoura section (8.5 km) as its Asatō Line on 26 March 1992.

The Gomen–Nahari section finally opened on 1 July 2002 — about thirty-seven years after the first groundbreaking and twenty-eight years after the Aki Line closed. It was the last of the public corporation's regional development and regional trunk ("AB") lines to open, apart from those whose construction was cancelled, and as of 2023 it was also the most recently opened non-electrified railway line in Japan, the Senseki-Tōhoku Line excepted. A fleet of stainless-steel 9640 series diesel railcars — "9640" can be read as "Kuroshio", as in the company's name — serves the line; the cars built for the opening included two open-deck observation cars with rounded, whale-motif ends.

Every station has an image character designed by the Kōchi-born manga artist Yanase Takashi. The characters appear as objets at the stations, as markings on the trains and on merchandise, and in 2004 a local citizens' group made costumes of them, which appear at events as the "Gotogoto Kigurumi-tai". The cast runs from "Gomen Ekio-kun", a station attendant at Gomen, to "Naha Riko-chan" at Nahari. "Aki Nurse-chan", the character for Aki General Hospital-mae Station, which opened in March 2021 after Yanase's death, was designed by Yanase's studio.

21 stations tracked on the map, listed alphabetically. Select any to read its page.

• Akano赤野
• Akaokaあかおか
• Aki安芸
• Aki General Hospitalあき総合病院前
• Ananai穴内
• Gomen後免
• Gomen-machi後免町
• Ioki伊尾木
• Kagami香我美
• Kyujomae (Kochi)球場前
• Nahari奈半利
• Nishibun西分
• Noichiのいち
• Shimoyama (Kochi)下山
• Tano (Kochi)田野
• Tateda立田
• Tonohama唐浜
• Wajiki和食
• Yasu (Kochi)夜須
• Yasuda (Kochi)安田
• Yoshikawa (Kochi)よしかわ

• 192211 April: the Muki–Gomen route is incorporated as a predetermined line under Table No. 107 of the revised Railway Construction Act, within the 'Shikoku Loop Railway' concept.
• 19573 April: the Asa Line is designated a survey line.
• 19599 November: the Muki–Gomen route is promoted to a construction line.
• 196422 April: the line is placed under the Japan Railway Construction Public Corporation as a works line.
• 196510 April: a groundbreaking ceremony is held for the Kōchi-side (Asa-sai) line.
• 19731 October: the Muki–Kaifu section (11.6 km) opens as part of the JNR Mugi Line.
• 1974End of March: the Tosa Electric Railway Aki Line (Gomenmachi–Aki, opened throughout in 1930) is abolished; April: construction begins on the Gomen–Aki stretch, including viaduct work.
• 1981December: construction of the Asa-sai (West Asa) Line is frozen under the Special Measures Act for the Promotion of JNR Management Reconstruction, with 18.9 km (about 44%) complete.
• 19868 May: the Tosa Kuroshio Railway is established, led by Kōchi Prefecture, to resume construction of the abandoned Asa and Sukumo lines.
• 198828 January: Tosa Kuroshio Railway is granted its Class-1 railway licence for the Gomen–Nahari section; 23 March: construction resumes.
• 199226 March: on the Tokushima side, the Asa Kaigan Railway opens the Kaifu–Kōnoura section (8.5 km) as the Asatō Line.
• 20016 December: track-laying on the Gomen–Nahari section is completed.
• 20021 July: the Gomen–Nahari section (42.7 km) opens as the Tosa Kuroshio Railway Asa Line (Gomen-Nahari Line), the last of the public corporation's 'AB' lines to open apart from cancelled ones.
• 20061 March: station numbers begin to be displayed at all stations on the line.
• 202113 March: Aki General Hospital-mae Station (GN27-1) opens between Kyūjōmae and Aki; its character 'Aki Nurse-chan' was designed by Yanase's studio after Yanase Takashi's death.