Fate/Labyrinth  

Manaka Sajyou, being linked to Akasha, lacks the ability to experience change or surprise. As such, she endeavors to "dream" by sending her consciousness beyond the World's boundary through its backside and into different time and space. She arrives in a maze with four Servants and Masters vying for the bottom. Manaka assumes the form of a Master who summoned a female King Arthur. Saber interacts with her, while she and the original Master can see each other when looking into a mirror.