Arahabaki is a useful Persona to have in the latter half of your Persona 3 Reload campaign. He's the ultimate form of the Hermit Arcana, which means you'll need the key item from the Hermit Social Link to unlock his fusion. Even if you have stronger Personas on hand or in the compendium, Arahabaki is used in several Fusion Recipes that you can use to create stronger Personas, such as Abaddon.