Read more about the line in English Wikipedia: Saikyō Line

Saikyō Line is the name used for a train service running between Ōsaki and Ōmiya. The name is an abbreviation of Saitama 埼玉- Tōkyō 東京.
As Saikyō Line uses tracks of other lines all the way, it's not considered as an official railway line. At this site the term "virtual line" is used for such lines.
The service runs parallel to Yamanote Line between Ōsaki and Ikebukuro, using the Yamanote Freight Line tracks, and is the only service using Akabane Line and the Tōhoku hon Line section Akabane - Musashi-Urawa - Ōmiya.

Akabane Line is usually referred to as Saikyō line as the line is used only by that service. Details about connecting lines etc. can be found in the Saikyō line section.

This section of the Tōhoku Hon Line is usually referred to as Saikyō line as the section is used only by that service. Details about traffic pattern, connecting lines etc. can be found in the Saikyō line section.