Illness
"So, what was your purpose of going there in the middle of the night, Augustine?" Maybe, this is the right time to tell them about my condition. "Let's focus first on our mission, Mushashi-san. Having a clouded mind when there might be possible combat wouldn't be beneficial to us," From how Augustine responded. He might have felt something was wrong from the conversation earlier at the rooftop.
"A piece of advice to the four of you. Being way too concentrated on the mission would increase the chance of failure. That is the way of your friend, Nicholas," Mushashi-san responded which he revealed Xavier's secret before going into combat. "I thought of that a lot in the past. How can Xavier easily overpower as if he didn't even have any difficulty facing hundreds of enemies?" Augustine answered and shared his thoughts.