The House of the Lost on the Cape is a Japanese novel written by Sachiko Kashiwaba. It was initially serialized in the Iwate Nippo daily newspaper from May 10, 2014, to July 4, 2015. Kodansha later published the novel in print with cover art by Yukiko Saito on September 11, 2015. An anime film adaptation by David Production premiered in Japan on August 27, 2021. The anime is part of the "Zutto Ōen Project 2011 + 10...", commemorating the 10th anniversary of the 2011 Tōhoku earthquake and tsunami.

A kappa —also known as kawatarō , komahiki , with a boss called kawatora or suiko —is a reptiloid kami with similarities to yōkai found in traditional Japanese folklore. Kappa can become harmful when they are not respected as gods. They are typically depicted as green, human-like beings with webbed hands and feet and turtle-like carapaces on their backs. A depression on its head, called its "dish" (sara), retains water, and if this is damaged or its liquid is lost, the kappa is severely weakened.