But the Yata can come in contact with it since it's a spirit that can detect anything astral. When Obito is in his Kamui form, the real body is in another dimension, but the replica is in the real world. That replica is formless. The Yata is also formless as well and it has been stated that it can defend against formless entities. So I'm going to assume that either the Yata doesn't permit Obito to pass through because it could spiritally yet magically travel to the other dimension, or it supernaturally transforms itself into the other dimension to deflect the astral entity.
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