OK, to get it from the top: This episode is a game promo, so it may be treated only as its commercial, or the anime series preview. It perfectly fullfills the requirements, but nothing more than that. Actually, it's slightly rescripted first episode, or vice versa, doesn't matter. If you seen the ONA, you don't need to watch the first episode, if you seen the first episode... you know the rest. Its benefits just like the first episode's — it catches you and doesn't let until the next dose of series It cannot be taken separately so if you've watched this, just know — you're on thehook