It isn't a spin off is a different retell like the movie is. They all run in parallel or continuum the manga, the 2d movie, the live action, the shitty 3d one; only the anime sac goes with the ova and would have arise as a prequel but some think it doesn't fit. The 1997 game would be a retell too but more based on the manga, all of the other games are tied to SaC.