Dear Past Me, Dear Future Me

One day, Mamoru comes home to find his boyfriend Aki's younger self sitting on his bed, and before he can even figure out what's going on, Aki comes home as well.
At first, they're all enjoying themselves with the situation, but as the differences between Aki and his past self only become all the more apparent, they're forced to confront uncomfortable and painful questions that have always been lingering in the backs of their minds.