These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Master Chief and Samus: He's a Space Marine, she's a Bounty Hunter. Both of them are clad in Powered Armor and weapons that they've used to annihilate alien invaders in first-person (Samus against the Space Pirates, Master Chief against the Covenant). On top of that, their arsenals also include energy weapons and explosives. Also a likely reference to Haloid.
Ivy and Etna: Both of them have some connection to dark forces, Etna being a demon, and Ivy tainted by Soul Edge. Their outfits are also veryVERYsimilar. Also a contrast, as Etna is rather flat-chested, and Ivy... isn't.
Holy Shit Quotient: Expect it to go through the roof whenever the game has a major update.