Yumi listens, silent. Vulpes has located a potential new senshi, Misaki Sakai. Middle schooler, about a year younger than they're assuming Yumi is. Recently moved to Natsuto. He can't make the offer immediately, and even once it's made, he likely won't accept an answer on the spot. The new girl gets time to think it over. In the interim, he wants both her and Elizabeth to pull bodyguard duty in shifts, with him watching over Misaki during the day.
"And just what are we guarding her from, that you want 24-hour surveillance by two high-end senshi?" It's here that the Guardian's unusual forthrightness stalls out, and some of that familiar reticence returns. He pauses for a moment, and Yumi can practically hear him deciding what to tell her.
"There is a faction of magical girls known as Executioners, fanatically dedicated to the prevention of any new senshi; if they discover Misaki Sakai, it is absolutely certain they will make an attempt on her life. They are extremely small in number, but each is exceptionally strong. Your raw power is extraordinary, Yumi Tachibana, but even the weakest Executioner would be slightly above you in magical strength, if not in skill. If one of the stronger ones were to appear, you and Elizabeth in tandem would be required to drive her off."
Yumi slumps back in her chair, in quiet shock. Senshi who want to kill other potential senshi. Which means she might have to fight another magical girl. "...why? Why the hell would they... is it a competition thing?" Vulpes shakes his head, and replies, "They are fanatics. There is little reasoning to be found in their goals. I would urge you not to attempt diplomacy, but I am quite aware of your nature. Regardless, prepare yourself for it to fail catastrophically when you do." He almost sounds apologetic.
Yumi lets out a soft huff. "...yeah, alright. I'm in. Just keep in mind I'm not gonna go all tight-lipped on her. If there's anything you 'forget' to tell her, I'll fill her in. I'm not buying into any of that 'we prefer the Guardian be the one to tell you' crap I got from Elizabeth."
Vulpes pauses, then replies simply, "I will bear that in mind," before turning in place and vanishing.