This is all the information I could find about 2006's Slash Dog after looking reviews on many sites.
* The plot is a Battle Royale style series. Tobio, Natsume, Samejima and the other survivors vs. the Utsusemi.
* Utsusemi are monsters who take the appearance of Tobio's classmates instead of being his classmates.
* Tobio’s parents appear. They were replaced with Utsusemi without Tobio noticing it.
* Sacred Gears aren’t mentioned at all. Jin is explained to be an animal with supernatural powers born from an egg (the same applies to Natsume and Samejima’s Sacred Gears)
* Grigori is replaced with a group of people who call themselves “Teachers” (先生, Sensei). Azazel’s role is played by a mysterious guy who calls himself “Third Teacher” (三番目の先生, Sanbanme no Sensei). This Third Teacher is the one who gave the eggs to Tobio and company.
* Either Sae and company are dead or Tobio didn’t rescue her on this volume, since she isn’t with the rest of the group at the end. (Someone was glad about this because it meant the childhood friend route was blocked).