In halo 4 Master Chief’s DNA was altered by the Librarian so that he was immune to the Composer.
In Halo Nightfall we see an element that can only kill humans, which operates like the halo rings, being weaponized by factions within the covenant.
There has also been biological warfare in recent halo comics. (I think, I haven’t read them, there seems to be some sort of biological weapon or something, can someone confirm?)
Now here is my theory. Master Chief is most likely immune to these biological attacks, as a result of what the Librarian did to him, just like he was with the Composer. 343 have promised that Halo 5 will be the darkest halo yet, and a massive biological attack on humanity is certainly a possibility for this. So maybe Locke is hunting for Master Chief who has gone rogue (presumably in an attempt to revive Cortana or find Halsey), in an attempt to reverse engineer this process.
So what do you think? Is this plausible?
Speculation is always fun!
P.S. Anyone notice the big robot thing from the halo 5 trailer in the MCC epilogue and intro?
I think this is a very good theory you have created here. I think though it might be the fact that he went AWL in the trailer for halo 5. So he is hunting him down to bring him back. get his mind clear again.
The only issue with that theory is that a new enemy/threat has risen and it’s a threat to both the UNSC and Swords of Shangheilios. I would imagine it’s a new enemy and not a substance. Besides, why would Jul’Mdama make the bioweapon harmeful to both himself and his warriors?
Edit: It’s an interesting idea though and a nice change of pace from the Medicant Bias and Precursor discussion.
The bioweapon from Nightfall and Escalation are likely unrelated. The only place that had the element that could kill humans was on the Alpha Fragment, yet Locke destroyed it. The bioweapon from Escalation killed Kig-Yar, so it likely could affect any living thing. One also doesn’t need the Librarian’s help to be immune from the Sedra bioweapon. plenty of normal people weren’t affected. So I doubt Locke is looking for Chief for that reason.