Spin-off books on supporting characters.

My list includes: Elide and Lorcan from "Throne of Glass" series by Sarah J Maas. Helene Aquilla from "An Ember in the Ashes" quartet by Sabaa Tahir. Tamlin from the "A Court of Thorns and Roses" series by Sarah J Maas. Grover from the "Percy Jackson and the Olympians" universe series by Rick Riordan. The Marauders from the "Harry Potter" series by J.K. Rowling. Magpie from the "Renegade" series by Marissa Meyer. Atlas Corrigan from "It Ends with Us/It Starts with Us" by Colleen Hoover. Zoya Nazyalensky from the "Shadow and Bone/King of Scars" universe by Leigh Bardugo. Lily and Tomas from the "Dread Nation" duology by Justina Ireland.