Negima!? Magister Negi Magi

Wait, You Can't do That, Negi! That's Right, Because We're Your Partners! (1x23)

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The Star Crystal Thief, posessing Evangeline through the Star Crystal, turns Asuna against Negi and many of his allies into stone. But with the help of his remaining students, he's able to defeat her by Pactio with the vampire, which (alongside Chachamaru), completes his Pactio collection but not get them out of trouble.