There was one rule that the thieves had to follow in this game. As much as possible, they should remain unseen and steal the target. Only then could they allow themselves to be seen and run to their escape vehicle.
And how could they remain unseen while their clothes were all the same? The answer was by using the extra ability all thieves had: Disguise.
They could disguise themselves as the NPC in the area and pretend to be one. This ability was also activated via a voice command that they could see on the edge of their vision. All the thieves have already been disguised and blended with the NPC in the targeted area.
The building they had to steal from held a party, and Sea Ring was one of the jewelry the host had in their office. To steal it stealthily, they needed a key that the host had and entered the office secretly.