Sylphia Island is a Ren'Py Visual Novel. You follow your named MC as he adjusts to life on the island after a accident causing him to lose his memory. You're taken into the home of Alex, a matriarchal figure who cares for 4 girls, Celeste, Lillian, Gracie, and Serra.
In order for you to be able to install this game, you need to enable (allow) installation of applications from unknown sources (Unknown sources) in the phone settings. Usually this item is in the Security section