the story might slap him with “SORRY THAT OPTION IS INVALID” in the future but he’s made his personal decision clear, and defended it through opposition.
armin is in super dire straits and eren begs him to hurry up!!! give the serum!! bertolt is right there, a shifter available for eating
it’s the perfect set-up for an injection. erwin is nowhere to be seen– dead for all he knows– but look at him. he’s silent, slow to respond, drawn in dark shadows, obviously unwilling, [edit:now that better scans are out, we see he’s in literal agony about having to do this lmao RIP] & when he FINALLY says “…fine” it’s with the face of a dead man. he DOES NOT WANT TO, but what else is there to do?
then erwin turns up on rescuer recruit’s back and levi is immediately transfixed. he doesn’t just pause in the act of handing the box over but quickly retracts his arm, presses it to his chest while staring very emotionally. at erwin. frozen again but so differently, god i need to breathe
eren goes “earth to captain???” and levi spares him one glance before helping erwin get settled. he checks for erwin’s breath even though the recruit already told everyone he was alive, just injured. he stands, visibly more composed now. he doesn’t even turn back to armin before announcing clearly, strongly, in bold
“the serum will be used on erwin.”
the contrast between that and his prior reluctant “ok” cannot be more stark
of course eren and mikasa are very upset at this! eren gets up in his face but levi replies, again in bold text, he’s going to choose for humanity. after saying at least twice before that erwin, specifically, is needed for humanity. whether his judgement in this is flawed/biased/clouded by feelings, it’s still his judgement
it clearly pains him to say this to the kids but there’s absolutely no indication that he changes his mind. not even the last look he gives mikasa: it’s the sad furrowed brow of a person who knows just how devastating this is for her, not someone coming to a sudden new revelation. their agony affects, but doesn’t sway him
levi chooses erwin, plain and simple. he always has.