Theory

Rui wasn't sure what to make of his first meeting with Master Reina Cara. She had shattered his impression of the legendary Silent Shadow one that nearly everybody had formed about her.

Still, she was the real deal. Knocking out everybody in the Shadow Isles manually just before the attack struck as an additional precaution to make sure that nobody saw her was an absurd feat that Rui had trouble wrapping his mind around.

It was worth partaking in anything she had to offer for him as an assassin. 

He followed her for quite a while within the vast infrastructure of the Area Crina organization before she finally reached an empty room. 

In its center lay a hatch on the ground which she promptly opened with a breathing technique.

Rui's eyes widened as his senses peered into an enormous cavity underground that the hatch led down to. However, he hadn't been able to sense the cavity underground with his regular senses at all.