Just as Filly said, there are many ways to recognize each other, there's no need to write words. Ash just needs to show a Heart Sword without harming the Sword Maiden, and she will immediately realize who the Starlight Body before her is.
Although this would break the Void Wings, due to the effects of Hell's Poison, the Void Wings have become a renewable resource for Ash. Breaking a Void Wing in exchange for the Sword Maiden joining the team is the most worthwhile sacrifice.
But will the Sword Maiden's joining be truly useful?
