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Technically the nature of Orihime's power is potentially very powerful as it is described as in its ways transgressing into Gods realm. Though Orihime is weak in will and determination. Rukia is a highly trained Shinigami of seat officer power level. Versatile and possessing of a good will and determination. So technically Orihime is the more powerful of the two and Rukia is the practical and realistically more powerful in practice.