Only team captains were granted aether letters, and the team captain assigned here was likely very busy with his own fights outside!
With the fake guards already there, this meant that there were already plenty of breaches. After surviving for so long, everyone knew that they did not depend on or wait for others this time.
The enemies must have wanted to kidnap them and turn them into hostages and shields. They would definitely make effective ones, since, unlike most territories, Alterra really did place emphasis on life.
Not to mention people, even the sentries wouldn't hit them if they surrounded themselves with Alterrans. What better meat shield to drag around than the 'weakest' Alterrans?
In a sense, this was really a good strategy!
The bastards even managed to copy the appearances of the uniforms, not knowing that because the Alterran uniforms were extra functional, there were inevitable variances in appearance that could be noticed by some sharp-eyed people.
