Miss Aimee didn't bring Gustav up to speed yet on what they were working on, but he knew she would eventually, so he didn't ask.
As days passed, Gustav would be the only one left in the abode, while Miss Aimee and Red Shadow would leave in the morning and get back in the evening every day.
He was still a bit intrigued by what they were working on, but he also had his mind on what he wanted to deal with, which was still back in Leoluch city.
When he was bored, Gustav would walk around the base checking different locations out, their training centers included.
During this time, Gustav broke through to the Falcon rank. He felt his strength increase a lot. If he had faced Zergeref in this state, he would have been able to handle it better.