Seishin Extension Line

The extension grew directly out of the original Seishin Line. The first stretch of Kobe's subway, between Shin-Nagata and Myōdani, had opened on 13 March 1977, giving the new western suburbs their first rail link toward the city. As development pushed further west into the hills, the municipal government planned a continuation beyond Myōdani to reach the heart of the rapidly growing Seishin New Town, and this continuation became the Seishin Extension Line.

Authorisation for the extension came in the early 1980s. On 17 February 1982 the Ministry of Transport granted the railway-business licence for the Myōdani–Seishin-Chūō section, and construction work on the segment began on 30 August 1982. Because much of the alignment ran across open hillside rather than beneath built-up streets, the works were dominated by surface construction interspersed with five tunnels.

The Seishin Extension Line opened in two stages. The first stage, from Myōdani to Gakuentoshi, was brought into service on 18 June 1985 — the same day that the Yamate Line's final link, between Shin-Kobe and Ōkurayama, was completed, joining the western and central subway sections into a single operation. Gakuentoshi ("University Town") took its name from the cluster of higher-education campuses developed nearby.

The second and final stage, from Gakuentoshi onward to Seishin-Chūō, opened on 18 March 1987, completing the extension and carrying the subway to the centre of Seishin New Town. With this opening the through route from Shin-Kobe in central Kobe out to Seishin-Chūō was finished, and Seishin-Chūō became the western terminus of the entire Seishin-Yamate corridor.

Service on the line continued to develop after it was completed. On 20 March 1993 a new intermediate station, Nishi-Shinminami, was opened on the extension between Myōdani and Gakuentoshi to serve further residential growth, and on the same date the new 3000-series trains entered service across the route. By this period trains were running through beyond the central end of the line: from 2 April 1988 the Kobe Electric Railway (later Hokushin Express Electric Railway) Hokushin Line had opened and begun reciprocal through services at Shin-Kobe, extending journeys north toward Tani-gami.

The line was caught up in the Great Hanshin earthquake of 17 January 1995, which severely damaged the Kobe region. Operations were suspended, then restored in stages: through running over the western section, including the Seishin Extension Line, resumed comparatively quickly, with the Itayado–Seishin-Chūō portion reopening on 18 January 1995 and double-track operation between Myōdani and Gakuentoshi restored on 25 January, while full restoration of the whole Seishin-Yamate route followed over the following months.

Today the Seishin Extension Line is operated as an integral part of the Seishin-Yamate Line and is rarely referred to separately in everyday use; from March 2000 the Kobe Municipal Subway adopted "Seishin-Yamate Line" as the unified guidance name for the combined route. The extension carries the western half of that line's traffic, linking the campuses, shopping centre and dense housing of Seishin New Town with the centre of Kobe, and its surface alignment across the hills remains a distinctive feature among Japan's mostly underground municipal subway lines.

• 198217 February: the Ministry of Transport grants the railway-business licence for the Myōdani–Seishin-Chūō (Seishin Extension Line) section.
• 198230 August: construction of the Myōdani–Seishin-Chūō section begins.
• 198518 June: the first stage, Myōdani–Gakuentoshi, opens (the same day the Yamate Line's Shin-Kobe–Ōkurayama link is completed).
• 198718 March: the final stage, Gakuentoshi–Seishin-Chūō, opens, completing the Seishin Extension Line to Seishin New Town.
• 19882 April: the Hokushin Express Electric Railway Hokushin Line opens and reciprocal through services begin at Shin-Kobe.
• 199320 March: Nishi-Shinminami Station opens on the extension between Myōdani and Gakuentoshi; the 3000-series enters service.
• 19939 July: rapid (kaisoku) service is introduced on the Seishin-Yamate route.
• 199517 January: the line is damaged in the Great Hanshin earthquake (Southern Hyogo Prefecture earthquake).
• 199518 January: service over the Itayado–Seishin-Chūō section, covering the Seishin Extension Line, resumes from 15:33.
• 199525 January: double-track operation is restored between Myōdani and Gakuentoshi.
• 20001 March: the combined route's guidance name is changed to "Seishin-Yamate Line".
• 201916 February: the 6000-series enters service on the route.
• 20265 January: one-man (driver-only) operation begins on the route.