In the Tokyo area, 3 non-JR lines turn into a JR line after specific stations.

・TWR Rinkai line (東京臨海高速鉄道りんかい線) in the direction of Shinjuku (新宿), Ikebukuro (池袋), or Omiya (大宮) becomes JR Saikyo line (JR埼京線), or either JR Shōnan-Shinjuku line (JR湘南新宿ライン) JR Sotetsu Shin-Yokohama line (JR相鉄新横浜線) in the direction of Ebina (海老名) after Otemachi station (大手町駅).

・Tokyo Metro Chiyoda line (東京メトロ千代田線) in the direction of Kashiwa (柏), Abiko (我孫子) or Toride (取手) becomes JR Joban local line (JR常磐線各停) after Ayase station (綾瀬駅).

・Tokyo Metro Tozai line (東京メトロ東西線) in the direction of Mitaka (三鷹) becomes JR Chuo local line (JR中央線各停), or in the direction of Funabashi (船橋) or Tsudanuma (津田沼) becomes JR Sobu local line (JR総武線各停) (the latter is from Mondays to Fridays during morning and evening rushes only).

・Tokyu Toyoko line (東急東横線) and Tokyu Meguro line (東急目黒線) become Sotetsu Shin-Yokohama line (相鉄新横浜線) after Shin-Yokohama (新横浜).

Technically the JR Chuo rapid line (JR中央線快速) becomes the Chuo main line (中央本線), but that's JR East transferring into JR Central, so that doesn't really count.