Most of the trains or subways here in the Kanto area have a Women Only train car during the 'rush hour' in the mornings. Seibu Shinjuku Line is no different.
On weekdays from 7:30am to 9:30am, the first car on the Seibu Shinjuku Line is a Women Only train car.
I always ride in this car for two reasons. For one, it's the nearest car to the station exit that I get off at. And the other, because it smells good. Especially in the summer. I'm not saying that men smell...but it definately smells better in the Women Only cars.