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Design
The 6000 series was developed for use on inter-running services to the Yurakucho Subway Line, as well as to be the basis for future Seibu Railway vehicles. The trains incorporate bolsterless bogies to reduce weight and complexity. Furthermore, the 6000 series fleet features variable-frequency drive (VVVF) traction systems. The all-over "lemon yellow" livery used with several older Seibu train designs was discontinued in favour of bodyside blue and white accents.

Most of the fleet was constructed using unpainted stainless steel, with fibre-reinforced plastic used for the front ends; however, between 1996 and 1998, eight sets were constructed using aluminium bodywork throughout. This change in material resulted in a per-set weight reduction of 14.1 tonnes over their stainless steel-bodied counterparts.

Internally, longitudinal seating is used throughout, with production sets being fitted with wheelchair spaces from new. All sets were initially built with LED passenger information displays above the doors.

Batches 1–4
The first 6000 series batch consists of two 10-car sets – 6101 and 6102. These were the first trains to use stainless steel bodywork in Seibu's fleet. The sets were built by Tokyu Car Corporation between 1991 and 1992 and designated as prototypes.

A batch of five production-ready 6000 series sets, numbered 6103 to 6107, first materialized in 1993, all of which were in service by 1994. For this batch, wheelchair spaces were installed in cars 2 and 9, and the side windows were modified so they would no longer be openable. Some portions of the driver's cab were modified to improve visibility. Since these sets were introduced, further design changes have been made, which are as follows.


 * Batch 3 (sets 6108–6112): This batch of sets was introduced in preparation for the opening of the "up" portion of the Seibu Yurakucho Line extension to Nerima Station. The first four sets were built with subway-compatible radio equipment, with the last of those four (set 6111) also being equipped with automatic train control (ATC). As set 6112 was initially deployed on Shinjuku Line services, it was not built with such equipment.
 * Batch 4 (sets 6113–6117): This batch of sets was introduced in 1995. There were minimal design changes over the previous batch of sets.

Batches 5–7
The fifth batch (sets 6151–6155) was manufactured from 1996. For this batch onward, aluminium was used for body construction. Additionally, Hitachi took over production of the 6000 series fleet. The manufacturer had supplied traction systems for earlier sets.

Batches 6 (sets 6156 and 6157) and 7 (set 6158) were delivered between 1997 and September 1998, featuring slight design differences over the preceding batch. To reduce costs and weight, these sets do not feature door-pocket side windows or front-end passing lights, and the bogie design was changed to incorporate a monolink system; the new bogies used in these sets were given the classifications "SS-150" for powered bogies, and "SS-050" for unpowered bogies. All subsequent trainsets would incorporate monolink bogies, with the exception being the 001 series Laview trainsets.

Operational history
The 6000 series was introduced into service on the Seibu Ikebukuro Line on 1 June 1992, and on the Seibu Yurakucho Line in 1994 following the latter's expansion to Nerima Station. While the 6000 series was predominantly used on Ikebukuro Line services, some sets were initially introduced into service on the Seibu Shinjuku Line.

As more trains were required to cope with the increase in capacity brought on by the introduction of Ikebukuro Line and Yurakucho Subway Line inter-running services, which commenced on 26 March 1998, some 6000 series trainsets were cascaded to the Ikebukuro Line and fitted with the equipment necessary for such operation. During this transitional period, some sets were unable to operate on the Yurakucho Subway Line. Therefore, these sets received yellow "S" markers on their front-end skirts to distinguish them from subway-interoperable sets and to prevent them from accidentally entering the subway line. Some sets were initially given green markers, but the colour used was eventually standardized to yellow.

Introduction onto the Tokyo Metro Fukutoshin Line
Ahead of the introduction of Tokyo Metro Fukutoshin Line inter-running services, twenty-three 6000 series sets underwent a refurbishment programme which ran between 2006 and 2010.

The refurbishment programme included the replacement of roller-blind destination displays with full-colour LED destination displays, the installation of external speakers, and the front ends being painted white (from silver). In addition, the driver's cab was remodeled; its original two-handle control system was replaced with a single-handle control system that combines braking and power controls. The driver's instrument panel was modified to accommodate a new train monitoring system, with two touch screens being installed – one on each side of the speedometer. These sets were also fitted with a number of safety systems, such as automatic train control (former Shinjuku Line-allocated sets only ) and automatic train operation (ATO). In addition, the LED passenger information displays originally featured in the fleet were replaced with 15-inch, double-screen LCD passenger information displays between 2008 and 2015. During the refurbishment period, unrefurbished 6000 series sets were affixed with "Y" stickers to indicate that they did not have the upgrades necessary for Fukutoshin Line operations.

Inter-running services between the Ikebukuro Line and Fukutoshin Line commenced on 14 June 2008.

Tokyu Toyoko Line/Minatomirai Line interoperation
On 16 March 2013, 6000 series trains were introduced on inter-running Tokyu Toyoko Line and Minatomirai Line inter-running services via the Fukutoshin Line.

Post-refurbishment upgrades

 * In 2015, sets 6156 and 6157 were experimentally fitted with new traction systems; set 6156 was fitted with a silicon carbide-based system with fully-enclosed induction motors, and set 6157 with an IGBT (insulated-gate bipolar transistor)-based system with permanent-magnet synchronous motors. The system used with set 6156 would be applied to all other Ikebukuro Line-allocated sets, and the system used with set 6157 would be the basis for the system used with the 40000 series trainsets.
 * From 2019, the onboard displays were replaced with ones similar to those of the 40000 series.