Oops, I Tamed the Commander Everyone Dreaded

On a sandy planet where humans live at the bottom, Lyra enters the Obsidian Palace for Kael the Commander's mate test to repay his boyfriend Ethan's gambling debts, only to discover she's the only fated mate to Kael. After that, Lyra foils the plot hatched by Serena, a scheming heiress to a great house, to destroy her, severs her ties with the once kind but now hard-hearted Ethan, and stabilizes Kael's dying star core successfully, being the only one he obeys on the planet.