after her husband's death, yui lives with her son. although he is a hikikomori, yui takes care of him. however, this is just a facade, as they have been aware of each other as members of the opposite sex since before her husband's passing. the feelings between the stepmother and stepson grow stronger each day, reaching their limit. yui decides to end this situation by inviting her son on a hot spring trip. although they are parent and child, they are essentially strangers. they want to be connected, both in heart and body. a storm of taboo pleasure engulfs them.