Then they might as well not enter and just stay honestly in the outside world.
That's why they kept trying to make a real tattoo.
"After the tattoo was successful, I selected some elites from the Chi Family and had them leave the Underground City to explore the outside world for news of extraterrestrial objects and seek opportunities to deal with them. Since we couldn't get any news from the outside world inside the gate, I wasn't confident of success and could only send people out continuously, even if it was just to preliminarily stabilize the situation outside," the City Lord said.
With a change in tone, the City Lord continued, "But this caused too much commotion and attracted the attention of other clans."
"This probably happened about sixty years ago. Seeing that the Chi Family could leave, they wanted to leave as well. When the Chi Family told them the reason, they learned that leaving could endanger their lives, so they stayed put."