Go-toubun no Hanayome Double Integral: Natsu no Omoide mo Go-toubun

Based on a manga "Go-toubun no Hanayome" by Haruba Negi, it features an original story where the Nakano quintuplets and protagonist Uesugi Fuutarou went to the Nakano's private island during the summer breaks just to found out that due to a heavy storm the group's can't go back home and has to spend 2 months in the island.