In the K novel series:

V.1 - Side: Blue - Focuses on the history of the blue clan and the events which led to Munakata Reisi's appointment as the current blue king. (Takes place before the anime, but after the events of K Side: Red)

V.2 - Side: Red - HOMRA in its early days and Anna's initiation to the clan.

V.3 - Side: Black & White - The silver clan between episodes 7 and 8 of season 1, focusing on flashbacks to Kurou, Neko, and Shiro/Weissman’s past.

V.4 - R: B - Suou Mikoto, leader of HOMRA, was strengthening his clan in Shizume Town. Munakata Reisi, the Blue King just enthroned, immediately reorganizes Scepter 4 and re-establishes order. When these two polar opposites meet, conflict is inevitable!

V.5 - Side: Green - Features Gojou Sukuna as the main character, and follows his rise through the ranks of JUNGLE.