[X] Pick up the weapon
-[X] Shoot and destroy the Reiquarium, here, no reason to kill Rei and Rei have no reason to kill Ritsuko
I hope this is a joke, because it's funny.
If it's serious, I'd like to apologize for treating it as a joke and remind you that the Reiquarium'd Reis are conscious enough to laugh maniacally. I don't know what would happen if Misato destroyed the Reiquarium, but the clone Reis probably wouldn't appreciate being shot at and there's no way Ritsuko left enough bullets in the magazine for all of them.
Also, both Ritsuko and Rei would probably object to this course of action.
Why shouldn't we pick up the weapon? All things considered, isn't it better to have a gun than to not have a gun?
Optics. If we pick up the gun, we're taking the power to shoot whoever we think needs to be shot. If we kick away the gun, we're definitively refusing the violent option, hopefully encouraging both Ritsuko and Rei to do the same, de-escalating the still uncomfortably escalated situation.
Personally, I'd do this sort of thing later - the immediate concern is de-escalation, and if Rei steps back a bit that then buys us a bit of leverage to use in the next write-in.
Hm.
Remember how Asuka accused Misato of favoring Rei? We
definitely don't want Ritsuko doing the same here. She doesn't have a literal gun any more, but if Rei doesn't shoot Ritsuko she could rat Misato and Rei out to Gendo, which is about equally effective as a weapon. Slower, but almost certainly more painful.
For that reason, and also because Rei's the one who still has a gun, we should probably focus on calming
her down. Ritsuko had a turn, and she can have another turn once Rei's calmed down.
[X] Write-in:
-[X] Tell Rei that you, too, are intimately familiar with the feeling of wanting justice for dead predecessors - your father's demise was the very reason you took up arms and joined NERV. Killing the Angels was your way of attaining it. But look where that has gotten you - you are an alcohol addict who marches children into battle, landed two of them in hospital and nearly got killed at the start of the last Angel attack. From someone who walks that path, you can attest to Rei that if she wants to live and keep the memories of her predecessors alive with her, starting down that road of revenge by pulling the trigger will not be conducive to a happy ending.
-[X] Remind Ritsuko that part of the reason Rei is pointing a gun at her now is as much for revenge as it is out of fear. If Ritsuko were to kill the current Rei, what would stop the next incarnation from eventually developing the same feelings about her predecessors' fates? Ritsuko would have to kill that one too, to stop her from taking revenge. And the next, when it happens again. And the next. You wonder if that wasn't the reason a number of the earlier Rei clones were killed to begin with.
--[X] You don't believe that Ritsuko truly wants to do that.
-[X] There's a chance to break that cycle now - but only if both parties agree to lay down their arms and make peace. If Rei can do what you could not and walk away from her revenge, if Ritsuko can accept that as proof that Rei is more in control of herself than Misato and is less deserving of death than you are.
[X] Do not
-[X] Rei, just like you, Ritsuko also deserves to feel safe which she cannot while you point a loaded gun at her - put down the gun first and then I will do so and collect both.
EDIT:
[X] Do not
-[X] Kick the gun away into a far corner of the room.
[X] Do not
I have my preference for which Do Not option I want, but lots of people want to intimidate Ritsuko for some reason