After allowing the ending to sit with me for a few days, I’ve realized that perhaps another way to look at things is to see it as a monumental indication of Big Boss’s descent into villainy. This twist basically means Big Boss has used one of his most trusted men as a pawn to further his own self-interests – rather hypocritical of him, considering that he left the CIA precisely because he wanted to create a nation where soldiers would no longer be used and manipulated by their higher-ups. He strips the medic of his identity, and forces him to carry on his legacy in the eyes of the public.
It’s very ironic stuff. The CIA used Big Boss as a pawn in their scheme to get their hands on the Philosophers’ Legacy back in Snake Eater, and they patted him on the back for it and rewarded him. Here, Big Boss uses the player as a pawn in his scheme to build his own Outer Heaven without us, and he pats us on the back for it, telling us we’re doing a good job. Big Boss essentially becomes the monster he used to hate.
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If that explanation doesn’t satisfy you, perhaps we can view the ending as a final ‘thank you’ from director Hideo Kojima to fans of the series as well. In the final cassette tape, Big Boss tells Venom, and us, that we, too, are Big Boss. We are also part of the legend that he’s created, and it all comes back to that iconic line from Metal Gear Solid back on the PS1: “The man is no match for the legend.” In a meta sort of sense, we (Venom) are seen as Big Boss’s right-hand man because we’ve been following and playing all the previous games in the series. We know Big Boss’s story better than anyone else; we know his moves. Given that, who better to take on the role of Big Boss than us, the players who have been following his story every step of the way?
