Harukana Machi-E

On his way back from a business trip, the protagonist decides on a whim to take a train back to his old hometown. The moment he pays respects to his mother's grave in the transformed town, he is transported back to a summer when he was still in junior high school, only with all his middle-age consciousness, knowledge and abilities intact.
On this journey across time, he understands for the first time the burdens born by his father, and his mother's tears. This is the kind of fantasy manga were made for, executed by an artist of great talent. This is a serious, delicate, and ultimately moving time travel variation.