Board Thread:Questions and Answers/@comment-26140824-20150228110725/@comment-25121259-20150308114628

Oh, I see, yes the narrow space, loophole or small gap, might be indeed what it is referencing. Specifically, it might refer to the fact that only the exact center of the Cauldron connects/leads to the Boundary, in a way it is a very small gap or a narrow place. In Phase Shift 1, Terumi utilizes that gap in order to enter Kazuma's body, so calling his next body a Loophole, which allows him to enter the world (more like exist in it in physical manner), makes some sense.