Natsu no Arashi! Akinai-chuu

Summary

The summer of a man's boyhood memories continue. Still on the cusp between childhood and being a man, he has linked with the ghost of a young woman from the World War 2 era. She, and the ghosts of other young ladies from that time, continue adventures alongside their linked partners, learning more about each other and travelling through time via their supernatural connection. While he struggles to see his crush on her come to fruition, meanwhile his friend—a girl his age, pretending to be a boy—seeks his attention as well.

(Source: Anime News Network)