Although I can't know where inspiration will take me in order to know which side book I will finish first, most likely it will be Conqueror of the Sun - Severed Galaxy as it already is at least halfway complete with over 170 pages. Besides just really enjoying the story myself, this side book will be quite important and unique compared to most of the other side novels.
Most of the Conqueror of the Sun side stories take place during one of the 7 main books. In fact, 20 out of the 23 planned novels take place in the same time frames as the base story. However, Severed Galaxy is a yet mostly untouched time period for the series. The tale takes place during the time mentioned at the epilogue of Conqueror of the Sun - Book 4 - Queen's Chaos as to give a detailed account (and not just a few lines) of the IRF attack on Earth and the start of the Galactic Civil War.
Other likely candidates for being the first side book finished first or at least the next one after Severed Galaxy are Conqueror of the Sun - The Dead Doll Princess (which takes place almost immediately after the end of Severed Galaxy) or Conqueror of the Sun - And It Lasted 100 Hours, which as mentioned in Book 5 - The IIIrd Tear is Shawn Arc's attack on the Atlon homeworld.
On a somewhat related topic, I feel I should explain that each side book falls under a predetermined style of story which I divide into "Chronicle" sets. Although all books will always have a lot of "story" and character interactions, those novels listed under the W.A.R. Chronicles and as the name implies will have more action scenes in the form of battles and combat. Contrasting to this, the Alternate Light Chronicles will have very few to none "war" type scenes and instead focus on character development and interaction stories.
And although I enjoy both style novels, hopefully this category system will assist readers in deciding which side book they may want to try reading once the number of side book stories increases and are published.
