After some thought, you conclude that there is really nothing you can say that will stop Altria from accompanying you to the meeting. The fact that you don't try to fight the British girl's self-appointed inclusion into this matter doesn't mean that you're about to bring along everyone you know - even if Kasumi and Ayane did discuss the meeting where a bunch of other people could overhear them, they only specifically invited you. Taking it upon yourself to bring four other people with you could be seen as rude, at least, if not openly distrustful. Altria, at least, has the reasonable excuse of being directly involved in the matter that's to be discussed; your other companions do not.
You're sorely tempted to bring Lu-sensei along anyway, if only for the sense of security he would provide while you are chatting with a bunch of ninjas, but that would leave Cordelia with only Briar for company - and while you'd be the last person to discount the fairy's value as a companion, you have to admit that there are a lot of situations in which a tiny person who is invisible to the majority of the population just isn't going to be as helpful to have around as an old guy who has clear adult authority, connections with the locals, and the ability to punch someone's lights out from across the room.
Cordelia, understandably, sees things differently, but Lu-sensei helps you talk her into staying with him and checking out the next round of the tournament. Briar takes a bit more convincing, until you suggest that she leave a tracking spell on you, so that she monitor your condition and location - and in the unlikely but still possible event that something goes wrong, lead Cordelia and Lu-sensei to you in a hurry. That appears to appease the fairy, at least enough to get her to stay with Cordelia.
Incidentally, you leave your various trophies with Lu-sensei, who somehow makes them all disappear up his sleeve, giant novelty check included. You have got to get him to show you how to do that - but later, later.
"Is there a particular reason why you are so concerned about Miss Chase's well-being?" Altria asks as the two of you leave the cafeteria. "Or are you simply protective of all your friends?"
"A little of both," you admit. "I do tend to look out for people close to me, but I'm not usually this proactive about it. It's just that a lot of things have happened in the last couple of days to put me on edge, on top of the whole being in another country thing, and I'd rather not take chances."
Altria nods. "So," she says, neatly changing the subject, "where is this meeting to take place?"
You pause in mid-stride. Did either of the ninja-girls ever mention that rather important detail?
...
Thinking back on it, you're pretty sure they didn't bring it up. There is no way that wasn't deliberate, which means...
You sigh, and raise your head. "You can come out now-"