Seibu Toshima Line

The line was a project of the Musashino Railway, the predecessor of today's Seibu Railway. The company applied for a railway operating licence on 20 September 1926 and was granted it on 30 October 1926, for a route in Shimo-Nerima village in the former Kita-Toshima District. An application to begin construction followed on 9 December 1926. The short branch was intended from the outset to connect the existing Musashino Railway main line (the present Ikebukuro Line) at Nerima with the grounds of a large new recreation park then being developed nearby.

Construction was authorised on 28 June 1927 and work began on 5 September 1927. The line opened on 15 October 1927 as the Musashino Railway Toshima Line, running the 1.0 kilometre from Nerima to Toshima Station. Its purpose was passenger access to the Toshimaen amusement park, which had opened nearby in 1926, and from its first day the line served essentially as a dedicated approach to the park and its surroundings.

On 1 March 1933 the line's outer terminus, Toshima Station, was renamed Toshimaen Station after the amusement park it served. The "Toshima" name is a historical one, derived from the old Kita-Toshima District in which the area once lay; neither Nerima nor Toshimaen Station is actually located in the modern Toshima Ward, a point Wikipedia notes explicitly. The renamed station fixed the park's name firmly to the railway it depended on.

Like the rest of the Musashino Railway, the Toshima Line was swept up in the wartime and immediate post-war reorganisation of Tokyo's private railways. On 22 September 1945 it became part of the Seibu Agricultural Railway (Seibu Nōgyō Tetsudō), the company formed that year by merging the Musashino Railway with the older (prewar) Seibu Railway. On 15 November 1946 the enlarged company took the name Seibu Railway, and the route became the Seibu Toshima Line, the form under which it has operated ever since.

In service the Toshima Line has long been operated as an extension of the Ikebukuro Line: its trains are local services that run through between Toshimaen and Ikebukuro, and at Nerima they connect with through trains to and from the Seibu Yūrakuchō Line. Because the line existed chiefly to carry passengers to Toshimaen, its fortunes were closely tied to access patterns to that part of Nerima. The opening of the parallel Toei Ōedo Line eroded its traffic: the subway's first section from Hikarigaoka to Nerima opened on 10 December 1991, it was extended from Nerima to Shinjuku on 19 December 1997, and the full loop opened on 12 December 2000, giving the area a competing direct link toward central Tokyo and contributing to a marked fall in Toshima Line ridership.

Station numbering was introduced across all Seibu Railway lines during the 2012 fiscal year. The two Toshima Line stations were given numbers prefixed with the letters "SI", the same prefix used on the Ikebukuro Line, formally designating the Toshima Line as a branch of that line. Nerima carries the number SI06, shared with its place on the Ikebukuro Line, while Toshimaen is numbered within the same SI series.

The amusement park that gave the line both its traffic and its name, Toshimaen, closed permanently on 31 August 2020 after some ninety-four years in operation, with its site later redeveloped to include a Warner Bros. studio-tour attraction and a public park. The Toshima Line itself remains in everyday service, still just one kilometre long and still worked as a through local service with the Ikebukuro Line, carrying local passengers and visitors to the redeveloped Toshimaen district.

• 192620 September: the Musashino Railway applies for a licence for the line; the licence is granted on 30 October and a construction application follows on 9 December.
• 192715 October: the line opens as the Musashino Railway Toshima Line, running 1.0 km from Nerima to Toshima Station (construction authorised 28 June, begun 5 September).
• 19331 March: Toshima Station is renamed Toshimaen Station after the adjacent amusement park.
• 194522 September: with the merger of the Musashino Railway and the prewar Seibu Railway, the line becomes part of the Seibu Agricultural Railway.
• 194615 November: the company is renamed Seibu Railway and the route becomes the Seibu Toshima Line.
• 199110 December: the parallel Toei Ōedo Line opens its first section, Hikarigaoka–Nerima, beginning the competition that would reduce Toshima Line ridership.
• 199719 December: the Toei Ōedo Line is extended from Nerima to Shinjuku, intensifying the loss of Toshima Line passengers.
• 200012 December: the full Toei Ōedo Line opens, completing the competing route toward central Tokyo.
• 2012Station numbering is introduced across Seibu Railway during fiscal year 2012; the Toshima Line stations are prefixed 'SI', designating the line as a branch of the Ikebukuro Line.
• 202031 August: the Toshimaen amusement park, which the line was built to serve, closes permanently after about 94 years.