Extremely long post incoming.
Here's my pitch for a new Halo trilogy:
Instead of playing as Master Chief, we play as a Spartan III.
The Plot is similar to 4, but from our perspective. Infinity is on one of the Halos, "decommissioning it", they find some forerunner signals that lead them to Requiem,
However, instead of finding the Didact (always found his shield world idea incompatible with the lore) they find the beloved flood-infected murder AI Mendicant Bias, or at least a fragment that is trying to rebuild itself.
The Storm Covenant obviously are helping mendicant out, and since most of MB's pieces are on the ark, it's trying to get there.
MC and Cortana are alive, and they do get sucked in the planet before infinity arrives etcetc. MC and Cortana are chasing MB through the planet trying to stop him from getting his requiem pieces and going to the ark. We (Let's use Undefined Spartan Fireteam for Clarity) the USF are attempting to keep the infinity ship whole, since the moment we arrive MB sends the storms, sentinels and even releases some flood that were in containment on the planet to overrun the infinity and stop us from helping MC.
The Infinity gets much more damage than in halo 4 here, it in really bad shape and is effectively overrun with enemy forces, by the end of the game the infinity manages to leave the planet with a more "skeleton-like" structure needing to go back to the UNSC for repairs.
The first game ends on the infinity leaving for earth with the USF left on Requiem, the last mission of the game is a "suicide mission" that allows the infinity to leave, but the remaining USF are stranded on the planet for now, by this point MB, MC & Cortana have already vanished to the ark, but we don't know that because we were busy trying to save humanity's strongest battleship (and only one of it's kind)
The second game has the remaining 3 USF regroup with some odst and marines, and attempt to survive on the planet, they find out what MC & MB were doing and where they went. They find out Requiem teleported to the ark due to MB's actions, and that the Spirit of Fire crew is down on the ark.fighting the banished (Halo wars 2 tie in), the second game ends with the remaking USF regrouping with the spirit of fire after finding a way to "nuke" requiem to get rid of the flood.
Also during the second game, Cortana starts to lose it almost completely and gets infected with the Logic plague (lore way the flood infected MB) but because she is damaged she doesn't defect to the flood.
In the third, we get the "New Prometheans" which arent decomposed hardlight human, but living sentient life altogether, here Cortana essentially becomes a robot version of a Grave mind but instead of biomass, she is turning everyone into Prometheans.
This is so we can get The weapon in the fourth game, cuz she's cute and I like her.
Cortana fucks off to human planets because she wants to "save" the humans by turning them into Prometheans, due to obvious ideological conflicts Cortana leaves MC behind (idk where yet, but he gets stranded somewhere), while she leaves for the outer colonies to slowly grow her army. The Infinity is almost done repairing, but to help out the USF and The Spirit of fire fight the banished, the UNSC send some a few of their frigates (same size class as the Pillar of autumn) the third game focuses on the USF fighting the Banished on the ark and remnants of requiem
The third game ends on a sad ending of the USF sacrificing themselves to prevent the banished from getting to earth.
The fourth game is a Master Chief game, it's a Halo infinite reboot/retcon, the Infinity gets repaired and leaves for the ark to end the banished, we get the whole MC vs Atriox, the infinity get fucking wrecked, Chief is stranded on the ark trying to regroup what's left of the UNSC and attempting to kill the remaining banished warlords. We get the same supporting characters, but, no Endless, it's too much. From here you start a new trilogy with the master Chief trying to end the banished and stop.cortana.
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