Games like Summertime Saga

If you finished Summertime Saga, the closest matches are Sex, Sen no Hatou, Tsukisome no Kouki, Miageta Sora ni Ochiteiku, Nami no Mani Mani - Sazanami Shinryoushou and Akujo Densetsu. All 6 share its adventure genre and are ranked by how closely their themes and modes overlap.