The D2 Rotor Bag consists of a CS2, inside which you will place the Drone Foam for the Mavic Mini, and of course the Pocket Cap Front to organize all the additional small stuff that goes with being a Drone Pilot, and finally the Pack Cap Rear, which allows you to choose whether you want the bag to be a backpack or not.
The D2 Rotor also includes a Main Handle and a Shoulder Strap. (Most of the time, it's nice to keep the backpack straps stowed away and just use the Handle and the Shoulder Strap.)
Note that this bag is pretty much the same as the B2 COMPUTE, except it has a Pack Cap Rear in place of the Flat Cap Rear.
Because it is possible to build larger configurations that combine multiple Center Sections (most of which include the CS4), and because the CS4 opens to the front, and because this CS2 is often zipped onto the back of a CS4 in larger configurations, this bag (the D2 Rotor) opens towards the rear.
As with any BrightLine Bag, the FLEX System lets you add other Center Sections at any time to build larger bags to serve all sorts of needs, as your gear requirements change from day to day. This bag (the D2 Rotor) is an awesome small starting point.