This is a recap special with behind-the-scenes material. It's not a story episode, it's a bridge for people already invested enough to buy the box set, and a chance for the production team to explain what they're building next. If you've watched Initial D up through Third Stage, this tells you nothing new about Takumi or street racing. What it does is let you sit with the people who made the show and watch them get excited about Fourth Stage before it exists. That's the real hit: not the racing, but the confidence in the room.
Bundled with the Fourth Stage DVD-BOX, this single special looks back over the Initial D anime so far. It recaps the events of First Stage through Third Stage, adds commentary from the production staff, and includes an early peek at how Fourth Stage was being made. The action, drama and sports moments of the earlier seasons are condensed into one release, a handy refresher before the next stage.