There are a few Nartia Express trains that stop in Ikebukuro but they are not very frequent. What happens is the train splits into two sections at Tokyo, one section heading to Shinagawa / Yokohama while the other section loops around to Shinjuku with its final destination at Ikebukuro. I have takien this many times to get to the Crown Plaza Metropolitan (by the way, I recommend that you not use PriceLine to get rooms here... just call the hotel direct if you have status with Intercontinental and you will still get a rate of about $100 + tax but at the same time earn points).