This is tough. MGS games had a ton of rivalries. There was Naked Snake Vs. Volgin, Boss, and Ocelot. Then there's Solid Snake Vs. Liquid, Big Boss, and Ocelot. Can't forget about Raiden Vs. Solidus. Vagrant Story meanwhile had a 3 way rivalry between Ashley, Sydyney, and Romeo. Heck, you can throw Jan Rosencratz in the mix.
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That's not a bad thing. That's a good thing. I like me, you like me, and I'm going to help you like you.