Amanozako is a curious demon looking for "someone" and volunteers to stick with the protagonist who has recently acquired the power of Nahobino and is wandering over Da'at cluelessly. 

The protagonist first encounters her being surrounded by a group of Preta who want to eat her before she gets them to take notice of Nahobino, pulling him into the conflict to save her. The person she is looking for is her father Susano-o. She's been searching for her "soulmate," although she temporarily breaks.