S-Train service was first announced by the four operating companies on 16 June 2016, with further details being given on 10 January 2017. The service is centered on Seibu Railway, and uses their 40000 series trains. Within the four operating companies, the S-Train is the first-ever reserved-seat train to operate on the Tokyu and Minatomirai railways. The name "S-Train" was used by the 4 companies during trademark registration on 21 November 2016, and has been trademarked since 21 April 2017. The "S" in "S-Train" stands for the following:
Scene: Used in different scenarios, like commuting to work, going to school or going on outings
Seamless: Seamless journey thanks to through service without interchange
The three terms above all start with the letter "S", hence the name "S-Train". The logo has three different colours, each with unique meanings. The upper part of the "S" is coloured green, signifying the greenery alongside the Chichibu Line; the lower part of the "S" is coloured blue, signifying the Minatomirai Line, whose signature colour is also blue; and the text "S-TRAIN" is grey, signifying the urbanisation around Shibuya and Toyosu, which the train serves. In terms of service type, the S-Train is uniquely positioned. It is positioned lower than Seibu's limited express on the Seibu service hierarchy, but is placed higher than Tokyu's limited express in Tokyu's service hierarchy.
Services
Train operation differs between weekdays and weekends. The direction is denoted by "Up" and "Down", where trains for Toyosu or Motomachi-Chukagai are "up" and trains for Chichibu or Tokorozawa are "down". This is based on Seibu's standards, in which southbound services are "up", and northbound services are "down". The S-Train follows Seibu's standards because it is the main operator of the service. A further reason for using Seibu's standards is to prevent confusion, as Tokyo Metro and Tokyu use reversed denotations of service direction compared to Seibu. Since all seats on the S-Train are reserved, there are special conductors to make sure passengers have purchased seat reservations. Because of this, the S-Train differs from regular Tokyo Metro services, as each S-Train is only operated by one person.
Weekdays
On weekdays, S-Trains operate mainly to serve commuters. They run between Tokorozawa and Toyosu, on the Seibu Ikebukuro and Yurakucho Lines, and the Tokyo Metro Yurakucho Line. There are 6 Toyosu-bound trains and 5 Tokorozawa-bound trains every weekday. S-Trains operate during the evening rush hours, except for one Toyosu-bound train which operates in early morning. The biggest feature of the weekday S-Trains is that it skips Ikebukuro Station, which is a core transfer terminal on the Seibu Ikebukuro and Tokyo Metro Yurakucho Lines, and is Tokyo Metro's busiest station. Another feature is that it operates as a limited stop service within the Tokyo Metro Yurakucho Line. S-Trains stop at Tokorozawa, Hoya, Shakujii-Koen on the Seibu Ikebukuro Line, and at Iidabashi, Yurakucho, Toyosu on the Tokyo Metro Yurakucho Line. According to :ja:S-TRAIN#平日|Japanese Wikipedia, the section between Iidabashi and Shakujii-Koen is so crowded that one cannot get on an S-Train without pushing into the carriage, regardless of the direction of the S-Train.
Weekends
On weekends, S-Trains operate mainly to serve visitors. They run between Seibu-Chichibu and Motomachi-Chukagai, on the Seibu Chichibu and Yurakucho Lines, the Tokyo Metro Fukutoshin Line, the Tokyu Toyoko Line, and the Minatomirai Line. The section is 113.8km, which is the longest distance of any Tokyo Metro through train service. There are 2 southbound trains, and 3 northbound trains per day on weekends. The southbound train from Hanno and the northbound train to Seibu-Chichibu are the only weekend S-Trains that operate in the morning. All other S-Trains operate in the evening. Passengers cannot board S-Trains at Ikebukuro.
