Oni no Iru Aida ni Watashitachi wa

Ashihara-san, who can see demons, meets Usui Azami, who is constantly victim of their attacks but can't see them. On the day of their meeting, Ashihara-san saves Usui-san from falling down the stairs by grabbing her hand, and that's when Usui-san realizes she can see the demons, but only when she's holding Ashihara-san's hand.