Once Upon a Blue Summer tells the story of Atasha and Kaiser, two individuals whose lives collide when Kaiser moves into Atasha's Villa "La estrella" in Cavite. Despite a rocky start, their initial animosity slowly transforms into a deep and meaningful connection, as they discover shared interests and values. However, unbeknownst to them, fate has its own agenda, and their journey together takes unexpected twists and turns, testing their bond in ways they never anticipated.