Note: I'm still for Mura's proposal for this update; not changing that. However I agree with SWB and Onmur that something needs to be said before we leave (assuming we're not staying here for this all to play out). So, in the same vein as Onmur's suggestions, I'll try tossing out various ideas on what we could say.
General form:
[] We're leaving her here with you. As much as I have problems with what Akiko has done, I don't hate her, and don't like leaving her like this. However there's nothing I can do to help her right now; I don't know enough about what's happened, nor do I have the history with her to be a welcomed face. She needs her friends with her to make sure she can make it out of whatever darkness she's buried herself in. Don't give up on her, don't let her deal with it alone, and don't leave her alone, no matter what she does or says.
~ Potential hints of having gone through this with Mami as well.
If the rest of the crew can't quite get their act together:
[] Is she your friend, or is she merely a responsibility — someone you were loyal to as your leader, but not particularly close to? Because right now, she needs her friends. And right now, that's not me; I can't help her out of this. I don't like what she's done, and I'll fight against her methods, but that's not relevant at the moment. Right now, she needs her friends to stay with her, listen to her, and care for her. Don't leave her alone.
If their friendship and loyalty remains strongly intact:
[] OK. Good. Stay with her; don't leave her alone. I don't think my presence would be welcome, and despite our differences, I don't want to actually hurt her, just stop her. I'd recommend keeping a constant watch over her, and always keep grief seeds handy, regardless of whether she says she's OK. Just... well, she's your friend; you understand.
If Akiko regains some lucidity:
[] We can talk about our differences later; now isn't the time. I don't like what you're doing, but I'm not trying to hurt you or kill you. You've got your friends here to support you, so let them. They're not going to abandon you — they didn't abandon you — so take some time to get your head straightened out. I know I have to do it from time to time, when I let my obsessions overtake my reason. Everyone has that bit of darkness inside them that threatens to swallow you whole; your friends are there to keep you from losing yourself to it.