On another hand, giving them any promises does not sit well with me either. Their leader looks like someone who would try to manipulate us if she gets a chance. How do you differ between a genuine request for help and using us as a tool to intimidate the rivals with?
For the moment I am wondering if we shouldn't leave Chizuka with the message 'if things go wrong, call me and I'll help', because she is the more honest of the lot, and is prone to impulsive actions... which means she won't wait until all hell breaks loose if she notices things are heading that way.
Of course, if she shares that information with her teammates (and she feels guilty enough to consider withholding it to be amoral), then they have another string to puppeteer us with.
It strikes me that Chizuka has seen first-hand how Yui reacts to people trying to kill her, and could therefore anticipate a similarly moderate response to other incidents. She'll know that calling for help from Yui is probably going to provoke Yui to find out what's going on and do something that we all think reasonable. I'd like to say that that's not the easiest response to exploit.
So, if we say something to Chizuka, let's not make any promises about what action Yui is going to take, more along the lines of "If your team get in trouble over your heads, call me and I'll do something at least as reasonable as I did when you ambushed me just now."
I don't want to get entangled in things outside Nagamioka when Nagamioka ought to have plenty of trouble to keep Yui busy in short order. Arguably, it already has that. However, leaving a message with Chizuka seems kind of useful as a tripwire for aggressive expansionistic groups. I could be persuaded otherwise pretty easily though.
[X] Continue attempts to negotiate with the Nerima girls in hopes of establishing some sort of agreement.
-[X] Ask for Maiko's read on the situation
-[X] Send Maiko and/or Minami off to search for calligraphy girl while you negotiate
-[X] "okay look, I actually was trying to do something before I got sidetracked here so I'll make this short: I'll leave you my contact information and with the promise that I will not interfere with your business if you don't interfere in mine."
-[X] "If you want to set up a more formal arrangement later we can do that. I'd honestly prefer it, but I won't force the issue"
[X] QBmail Chizuka: "Listen, you've seen that I can be reasonable. If you or your team get in over your heads, contact me and I'll be at least as reasonable with them as I was with you."
No red in your username or your avatar: You don't currently qualify.
Avatar is
Akane Tsunemori, in which Akane is apparently translated as "red."
Maiko offered to teach Yui microexpression reading a little ways back. That would come in handy just now, and maybe give an 'in' for developing the information-as-power aspects of Yui's magic for situations just like this one, with hard-to-read girls who might be a problem later.