Actually, from the very beginning, He Ao realized that something was off about "Liu Nan."
This feeling of wrongness wasn't because he found some specific problem, but rather, he always felt in his subconscious that everything was developing too logically.
Although he believed in Liu Nan's intelligence, the fact that an F-rank non-combat personnel could figure out the weakness of at least a C-level Beetle exotic beast and easily come and go under their watch in just half a day was reasonable, yet perhaps a bit too astonishing.
This seemed plausible, but it was inevitably a bit too eye-catching.
He Ao, with his D-level top strength that could compete with C-level when bursting, couldn't ensure that he could achieve the same.
This was actually the limit of the monster that transformed into Liu Nan's abilities; she could only transform into the person who was 'most supposed' to be there.