Nippori station is located in Arakawa ward, Tokyo. The part of the station is located in Taito ward. 3 operators are using this station. JR East, Keisei and Toei.
Foreign tourists use this station in case they travel to/from Narita airport by Keisei trains. Keisei operates limited express called Skyliner which connects Narita airport and Keisei Ueno stations. Skyliner stops at Nippori station which is next station of Keisei Ueno.
Then, most of the passengers of Skyliner transfer to other lines at Nippori rather than at Keisei Ueno due to Keisei Ueno is not adjacent to Ueno station which JR and Tokyo Metro operate. You have to walk couple of minutes outside to reach Ueno station.
After taking Skyliner from Narita airport to Nippori, most of the passengers change to Yamanote line or Keihin-Tohoku line. There are many passengers who head toward Ikebukuro or Shinjuku stations which JR's limited express Narita express stops. The biggest reason is that Skyliner is much cheaper and faster than Narita express.