Mobile Suit Gundam: The Witch from Mercury

Suletta Mercury attends the Asticassia School of Technology at her mother's request. The school uses duels to settle disputes, with the top-ranked duelist winning the right to marry Miorine Rembran as decided by her father. Suletta defeats Guel Jeturk, the current top-ranked duelist and Miorine's fiancé, but her victory is overturned when she's suspected of piloting a forbidden mobile suit, the GUND-ARM.