In/Spectre Temporada 1 Episódio 11

Kotoko came up with three solutions, but they all got shot down. Kuro keeps trying to grasp the future where they can defeat Steel Lady Nanase, but Rikka made it disappear once again. But Kotoko wasnt done yet. Steel Lady Nanase is not a ghost. What is Kotokos 4th solution that may finally put an end to Steel Lady Nanases existence once and for all?