1x8 - The Night Beyond the Tricornered Window

In order to learn more about Sensei's movements, Mikado and Hiyakawa make a plan to astral project into his house with the help of Mukae, Erika, and Sakaki. But they discover that Sensei's house was built on the site where the Palm of the Hand Research Society used to stand. Mikado recommends that they call off their plan out of concern for Hiyakawa, but Hiyakawa calmly replies "I won't remember. I never forgot."