My Elder Sister is the Universe

Every summer, our young protagonist eagerly anticipates his visits to his grandparents' house, driven by a powerful and simple motivation: his deep affection for his cousin Aoi, who resides with them. This particular summer, he finally summons the courage to lay his heart bare and confess his feelings to her. What unfolds is a sweltering and intensely memorable season, defined by intimate moments and the cherished experiences he shares with Aoi, whom he often affectionately regards as his older sister.