Cook oil and achiote seeds in a small saucepan over medium-low heat until oil turns dark red, about 5 minutes. Strain into a jar and let cool.
(** Note: The achiote oil can be made up to 1 week ahead. Cover and chill)
Heat achiote oil and butter in a large skillet over medium heat.
Add chiles, garlic, calamansi juice, and soy sauce and cook, stirring, until fragrant, about 30 seconds.
Add shrimp, season with salt and pepper, and cook, tossing often, until shrimp are opaque throughout, about 4 minutes.