Thread:B214/@comment-25223585-20150607033139/@comment-1359322-20150607034017

That fake Ise is still result of the curse Loki placed on both Rias and Issei. Issei's curse is seen when he entered JD last episode.

Rias' curse is her jealousy over the other girls' closeness to Issei and her desire to monopolize him. So that curse after having her tears touched Issei's scale mail created another Ise, which fits everything she wants from Ise. Understanding her, love only her, able to comfort her, as a result she became entranced with her own desire or in this case darkness and weakness of her heart.

Hence why she was so easily manipulated.