Preheat oven to 375 degrees F (190 degrees C). Line a baking sheet with a silicone baking mat.
Whisk sugar and Chinese five-spice powder together in a small bowl. Beat egg and water together in another bowl.
Melt butter in a large skillet over medium heat. When the butter foams, arrange peaches in a single layer in the skillet. Pour sugar mixture over the peaches; cook, turning peaches once, until sugar is melted, bubbling, and syrup has a tan color, about 2 minutes. Transfer peaches and syrup to a bowl to cool completely.
Cut pie crusts into eight 4 1/2-inch rounds. Set rounds on prepared baking sheet and fold edges of each crust up to form a 1/2-inch rim. Brush each crust with egg mixture.
Place 2 peach slices, pit-sides facing each other, in the center of each tart. Place 1 peach slice in center, skin-side up, in between the other two peaches. Drizzle excess syrup over the peaches.
Bake in the preheated oven until golden and bubbling, about 15 minutes.