Seibu Railway will introduce a new limited express train with a "new and unprecedented concept" in fiscal 2018. The train design will be handled by architect Kazuyo Sejima.

The 56 trains, consisting of seven eight-car sets, will be the company's first new limited express train in 25 years since the currently operating 10000 series "New Red Arrow." They will become Seibu Railway's flagship trains.

The design concept and the interior and exterior designs will be handled by Kazuyo Sejima. Sejima, a globally active architect who won the Pritzker Prize, known as the Nobel Prize of architecture, with the architectural firm SANAA, served as general director of the 12th International Architecture Exhibition, La Biennale di Venezia, in 2010. She has also worked on the architecture of the 21st Century Museum of Contemporary Art, Kanazawa, and the Louvre-Reims branch in France. Unlike previous designs which sought sharpness and style, the design of the new train expresses gentleness and softness that blends into the natural scenery.

Regarding her role in the design, Sejima commented, "I was approached to create a new type of express train that had never been seen before. This is of course my first time designing an express train, but I think the biggest difference from architecture is that it can run in a variety of places. I thought it would be great if the express train, which runs through a variety of landscapes, from the mountains of Chichibu to the streets of Tokyo, could blend gently into the scenery. I also hope that it will be an express train that is like a living room where many people can relax in their own way, one that makes people want to ride it again today."