The military of the Eldar Craftworlds is divided into two large branches. The first is the Guardians, drafted eldar citizens given basic wargear and training who serve in times of need. The second is the Aspect Warriors, a number of warrior castes whose paths are followed to completion as one the phases of an eldar’s life.
Each Aspect is based on a different facet of the eldar war god, Kaela Mensha Khaine—with one exception. In eldar mythology, the Crone Goddess Morai-Heg made a deal with Khaine: if he cut off her hand (so that she could drink her own mystically-powered blood—only Khaine had the power to harm a god in such a way), she would grant the power of her ill-omened daughters the banshee to Khaine.
The Howling Banshees are the elite assault troops of the eldar military. Each wears a specially-designed helmet that weaponizes their screams, scrambling opponents’ minds and attention as the Banshees deliver their blows. Their Exarchs wield some of the finest melee weapons available to the eldar, and they can exhort their squad to awe-inspiring feats of murderous speed in battle.
Since most Aspects are based on the masculine war god, most Aspect Warriors take on a masculine guise while they follow their path, regardless of their natural sex. The origin of the Howling Banshees, however, means that they are associated with women and femininity; male followers don women’s breastplates, becoming indistinguishable from their fellow Banshees under the armor.
(Here we also see the tau at their weakest. For multiple reasons—partially because the structure of their eyes makes it difficult for them to track moving objects, partially because tau tactical doctrine emphasizes the neatness and technological prowess involved in overwhelming firepower to brutal and primitive melee combat—the tau are very unskilled in close-quarters fighting. They have some of the longest-ranged weapons in the galaxy, and are quite happy to stay at those ranges.)