Bring 4 cups of water to a rolling boil in a medium saucepan over high heat.

Gradually add the tapioca pearls, stirring constantly for 2 minutes to prevent sticking, then reduce heat to medium and cook for 12–15 minutes until the pearls are mostly translucent with a small white center.

Remove the pan from heat, cover, and let the tapioca rest for 10 minutes so the centers finish cooking and turn fully translucent.

Drain the pearls through a fine-mesh strainer and rinse under cold running water, then transfer them to a bowl of cold water to keep them from clumping.

Peel the mangoes, reserve 1/2 cup diced pieces for topping, and place the remaining mango flesh in a blender.

Blend the mango until completely smooth (about 30–45 seconds), then add coconut milk, evaporated milk, and sugar; blend again until the sugar dissolves and the mixture is uniform.

Drain the tapioca pearls thoroughly and fold them gently into the mango cream mixture until evenly distributed.

Transfer the mango sago to a container, cover, and refrigerate for at least 2 hours until well chilled.

To serve, divide the chilled mango sago among 4 glasses or bowls, top with reserved diced mango, mint leaves, and pomelo segments if desired, and drizzle with extra coconut milk for garnish.