While on their quest to stop the Demon King, the violinist Hamel, the pianist Raiel, the magess Flute and the female warrior Sizer stop in a small kingdom and destroy a rampaging monster. While giving the four a heroes' welcome, the king and queen explain that their daughter has been kidnapped by a monster living in a nearby castle. They agree to go and rescue the hostage princess and defeat the monster. However, the enemy's castle is heavily guarded... (Source: ANN)

Trouble arises in Staccato one day. Demons show up and start to wreak havoc on the townspeople. The entire country seems to be suffering. The source of the problem is that the barrier which until now has kept the demons from crossing over to the human world, is weakening. The person who sustains it is losing her strength after holding it up for so many years. That person is Queen Horn of Sforzando. Hell King Bass is trying to break through the barrier and release their supreme leader, Kestra (Orchestra). One whose power is unparalleled yet is trapped somewhere in the world of the humans. (Source: AniDB)

It is the year 2046, Noboru Terao and Mikako Nagamine are close friends who will soon be graduating junior high school. But after an alien attack on humanity, Mikako is selected for the UN military space expedition set to retaliate against the aliens. Separated, Noboru and Mikako attempt to keep in touch by sending emails to each other with their cell phones. Yet as the expedition journeys farther from Earth, the time it takes for them to transmit and receive each other's messages increases substantially. Hoshi no Koe revolves around the relationship between this couple as they try to stay connected despite the growing distance between them.