Divide the Rice Chex cereal evenly among 3 large bowls, about 1 cup in each bowl.

Place the milk or semi-sweet chocolate chips and 1 tablespoon butter in a microwave-safe bowl. Microwave in 20–30 second bursts, stirring between each, until melted and smooth.

Pour the melted chocolate over the first bowl of cereal. Gently fold with a spatula until all cereal pieces are evenly coated.

Transfer the coated cereal to a large zip-top bag, add 1/2 cup powdered sugar, seal, and shake until all pieces are well coated and no sticky spots remain. Spread on a baking sheet to cool.

In a clean microwave-safe bowl, add 4 oz white chocolate chips and 1 tablespoon butter. Microwave in short bursts, stirring between each, until melted and smooth.

Stir in the vanilla bean paste until evenly distributed, then pour over the second bowl of cereal. Fold gently to coat all pieces.

Place this vanilla-coated cereal in a clean zip-top bag, add 1/2 cup powdered sugar, seal, and shake until fully coated. Spread on the baking sheet to cool.

In another microwave-safe bowl, combine the remaining 4 oz white chocolate chips and 1 tablespoon butter. Microwave in short bursts, stirring until smooth.

Quickly whisk in the strawberry agar-agar powder until the mixture is smooth and evenly pink, then pour over the third bowl of cereal. Fold gently to coat all pieces.

Transfer the strawberry-coated cereal to a clean zip-top bag, add the remaining 1/2 cup powdered sugar, seal, and shake until fully coated. Spread on the baking sheet to cool completely.

When all 3 flavors are completely cool and dry, gently combine the chocolate, vanilla, and strawberry cereal clusters in a large serving bowl and serve.