A Halo and RWBY fanfic could be a multiverse travel story, or he just stays in RWBY. Our main character wishes to have the abilities of Master Chief all his strength, combat abilities, and skills you name it practically becoming master chief himself. He also wishes for the AI Cortana to help him with the store, among other things. He wishes for a Halo shop system (now just a heads up I haven't played the latest game in the Halo series and it's been years since I played one so I might be off about weapons and armor abilities I did look up some things while writing this but I'm mostly going off my memory I'm to lazy to go all out in scouring through multiple wiki and forum sites for everything) in the shop he can purchase new weapons, ammo, vehicles, armor ability upgrades like making the stealth ability last longer the drop shield becomes bigger and regenerates more health you get the idea, as well as actual physical armor upgrades he starts with master chiefs basic armor he can later on purchase armor with thicker plates giving him more protection thinner armor so he can move faster or armor with attachment points for more ammo and grenades basically the multi-player armor customization of Halo Infinite. The system will also give him an inventory where he can store everything from armor, weapons, ammo, and vehicles but he will have mags attached to his armor because it will be quicker to get them than wait for them to materialize from his inventory or not upto whoever writes this story, some vehicles can be stored back into his inventory but some can't if this story goes multiversal he could use any of the spaceships in the Halo series but I'm partial to The UNSC Infinity-Class Supercarrier of the humans and the reason being the ships are massive and why would he store them back in the inventory the shop can either provide a crew or modify it so everything can be run by our main character with the help of AI. He is sent to Remnant a couple of months before the story begins, he's also the same age as Yang, so he can familiarize himself with his weapons and grind for cash for the store although he will start with the standard MA5 rifle and M6 pistol in the store the weapons are set as most human weapons are the cheapest as well as their ammo the covenant comes next and then the forerunner weapons are the most expensive same with vehicles, money is received from defeated enemies by killing grim and monsters or beating up crooks like if he goes to the DC Universe anything that would be considered defeating an opponent. He will choose one armor ability to start with but can purchase the others in the store maybe he will get aura and a semblance I mean he has the armor abilities and the armors normal regenating shield but it's upto whoever writes this story as I said before. I think it would be cool if he gets like a RWBY mechashift weapon with the Halo energy sword as a part of it it could be a rifle or sniper with an energy sword bayonet that can change to a pole type weapon like a spear or scythe, or into a sword. Some scenarios for world traveling I can think of are after the defeat of salem him and team RWBY and whoever else who will travel with him during a world transport the space fluctuations caused by the MCU Infinity cube during the avengers movie will drag the ship out of transport and our mc and the gang will help in the battle maybe stick around for a bit explore the space of MCU help around the world or just head off to the next adventure.