The Kuramoto family is a three-generation family consisting of Eri, her son and daughter-in-law, and their grandson Kameji. Kameji was raised by his grandmother Eri since he was a child, in place of his son and daughter-in-law, who are both busy working. One day, everyone decided to go on a trip to a hot spring to celebrate Eri's 60th birthday, but on the way, things started to look ominous for the son and daughter-in-law, who are still as busy as ever, so Eri and her grandson decided to go to an inn by themselves. When they arrived at the hot spring...