add_mutual_gendered_blood_sibling_hook_effect

add_mutual_gendered_blood_sibling_hook_effect = {
	# First we do current scope.
	if = {
		limit = {
			$TARGET$ = { is_female = yes }
		}
		add_hook = {
			target = $TARGET$
			type = blood_sister_hook
		}
	}
	else = {
		add_hook = {
			target = $TARGET$
			type = blood_brother_hook
		}
	}
	# Then set target's.
	save_scope_as = blood_sibling_self
	$TARGET$ = {
		if = {
			limit = {
				scope:blood_sibling_self = { is_female = yes }
			}
			add_hook = {
				target = scope:blood_sibling_self
				type = blood_sister_hook
			}
		}
		else = {
			add_hook = {
				target = scope:blood_sibling_self
				type = blood_brother_hook
			}
		}
	}
	# Clean up after ourselves.
	clear_saved_scope = blood_sibling_self
}

As written in game/common/scripted_effects/00_hook_effects.txt.