>>51158372They're not coded, but every box legend has a gender as Game Freak see them.
>Ho-Oh based off the Fenghuang, an explicitly female deity>Kyogre described as mother of the ocean>Dialga Lord of Time, like Father Time>male Zekrom/female Reshiram per picrel>Xerneas' ability to give life an explicitly female ability>Solgaleo/Lunala explicitly described as male/female with an evolutionary relationship>Zacian/Zamazenta explicitly described as male/female with a sibling relationshipTaking that on board, along with design themes and styles used in all the designs and their names (which like all other Legendary/Significant pokémon names remain the same across all languages), Koraidon is the male due to its harder lines, edges and angles bolder colour scheme and hard K sound in its name, with Miraidon's softer curves and flowing lines, muted colours and softer "Mi" sound in its name indicate it's going to be a girl. Given of late they've also related the legendaries to each other in some fashion, after seemingly exhausting themselves with opposites, it points to them being similarly related to each other's species.