In stories of people who swap bodies, they always return to their rightful places. But what if that never happens? Unfortunately, this is the exact predicament Yui Ootsuka and Yuuta Kimura find themselves in.

One day, after Yuuta comes crashing down on Yui from the treetops, both children find themselves in an unfamiliar body. But no matter how desperately they try, they are unable to revert things to how they originally were. In the end, they settle with going about each other's lives as if nothing had happened, determined to keep the incident a secret. Though merely classmates in the past, this inexplicable accident binds their fates tightly together.

Shishunki Bitter Change follows Yui and Yuuta through the years as they struggle through a life that is not their own. In this wearisome situation, the two of them discover what it truly means to walk in someone else's shoes.