Minami Sakuta (2nd grader at high school) is in the school swimming team. An avid fan of an anime series called "Buffalo Koteko is the Magical Plasterer," she has a fateful encounter with another "Koteko" fan and a classmate, Shohei Moji. Minami has a nice stepdad and can't remember her biological father. A year ago, Minami received a handwritten talisman from an anonymous sender. Shohei's brother helps Minami solve the mystery and find her biological dad, who is a cult founder. She decides to meet him. Minami pretends to attend a school trip so she can visit her father in a seaside town. Shohei can't stop worrying about Minami as the adventure of her life begins.