Everything can be covered in shadow.  This is the significance of C.S. 13.  Two players appear beneath the Ikaruga no Kagami with no real recent memories.  Ikaruga uses that as a chance to move forward, “What should I do?”
An original novel derived from .hack//G.U.  Pushed forth by original characters, it takes place between volumes 2 and 3.  Warning, while the main story remains the same, AIDA’s setting, the twilight epitaphs, Harold, and others have been tweaked.

Raws: http://ncode.syosetu.com/n9638j/
Author: 月京蝶  (Moon’s Imperial Butterfly)
Translator: Gandire Alea
Chapter List:

  1. Character Introduction
  2. The Water Capital, Mac Anu
  3. Chaos Gate
  4. Shinigami X Shinigami
  5. Dreams and Reality
  6. First Experience
  7. The Invisible Cage
  8. A Wounded Bird
  9. A Cat and a Monk
  10. The R.A. Project, Ito’s Report
  11. Shinigami X Shinigami, Again
  12. Drifting
  13. Skeith
  14. Invasion
  15. Seeking Revenge
  16. Stumped and Resting
  17. Home
  18. AIDA
  19. Sense of Defeat
  20. Reunion
  21. Shirakawa Junya
  22. Forfeit (or Defeated)
  23. Bloodstained Dirt
  24. Half body (or Half length)
  25. United Front
  26. Those Who Survived
  27. Her Memory
  28. Favorable Wind
  29. Report
  30. The Third Focal Point… of Power
  31. Shinigami V.S. Shinigami
  32. One Person, Two Characters (or roles)
  33. Eve of the Decisive Battle
  34. The Ringleader
  35. A Smile from the Goddess
  36. 9 Pickup 9  (九拾九?)
  37. The Time Remaining
  38. The Conclusion
  39. Selfishness (Willfulness/Disobedience)
  40. Their Respective Sins
  41. Self-Reliance
  42. Thrice (Mitabi), Shinigami X Shinigami
  43. C.S.  -Epilogue-
  44. Afterwards + α