Kisetsu no Hanayome

Kise, the protagonist, is an orphan who lives happily with his adopted family: his older sister Natsumi, his mother Asuka, and his younger sister Hazuna. One day, at the traditional festival in the village, he meets a mysterious girl in the hills of the village, Maki, a girl without memories who wants nothing else but to become his bride. [Shortly translated from Getchu]