Yui Hayakawa is a lazy and idle young lady who finds joy in sleeping and eating. Despite her age of 16, she looks like a young boy from elementary school. Her only skill is her impressive running speed. While activating her little brother's time machine by accident, she gets whisked away to the Sengoku era. Fortunately, she joins a cluster of withdrawing soldiers under the alias of Yuinosuke. Later, after consuming some mushrooms, she finally meets the man of her dreams.