Struggling with asthma and social isolation, young Anna Sasaki moves to the countryside for a fresh start recommended by her doctor. Immersing herself in drawing, she stays with relatives near the sea, stumbling upon the enigmatic Marsh House. There, she encounters Marnie, a mysterious girl who sparks a transformative friendship, revealing hidden secrets within the mansion. Through their bond, Anna unravels the mysteries of the past, embarking on a poignant journey of self-realization and cherished memories in 'Omoide no Marnie'.