"The choice of whether you join us on missions or not is yours, Ai. I can take measures to ensure someone's by your side at all times... or assign you tasks that keep you away when the fighting starts. But at the end of the day the choice is yours."

Whether she stays on the train, joined another team or stayed with them, he wasn't going to force her hand. He couldn't guarantee her safety if she stayed on the train or joined another team, but he could sure as hell try if she remained on blue. But he also had to admit that he would rather have the younger, untrained kid stay as far away from the action as he could get them. That didn't always work though.