The multiverse. An infinite collection of universes, each different in its own way. All independent from each other, unable to interact with each other.
Through a peculiar anomaly in space and time, the universes of the Bravoverse collide. Soon, Task Force Bravo shall meet face to face with a rookie squad of Army Rangers, the Empire's Jedi hunting crew, the Colonial Marines, even the band of survivors of Sevastopol.
Croft: Bravo, we still don't have any idea what the hell is on that planet, but we suspect that it might be crawling with Covenant. Your mission is to investigate the surface and report back anything you see. Lieutenant, is everybody accounted for?
Hartley: Yes, sir.
Croft: Good. Gear up and get to the HEV bay, you'll drop in a few minutes.
UNSC Ticonderoga speakers: 37th Airborne to the cryopods. Repeat, 37th Airborne to the cryopods. Preparing to enter slipstream space.
Hawkins: That's our cue.
The 37th leave their canteen tables and make their way to the cryochamber.
Hawkins: Rangers, you should all know the mission, but here it is again: we are to make the first UNSC incursion onto a newly-reported planet in the Crux Majoris system. Home intelligence reports possible signs of life. Even if these are false, there's no doubt that the planet could become a UEG colony. Rangers, to the pods.
The group of Rangers disperses, entering their cryopods.