You may have died or maybe someone threw your soul outside your body severing your soul chain in the process. Whatever happened now you possess the power of Shinigami. You have bonded with an Asauchi, which will transform into your Zanpakutō when you gain the name of your inner spirit. You are also trained in the four core techniques of the Shinigami which are Zanjutsu, the art of sword fighting, Hakuda, unarmed combat, Hoho, mobility techniques and Kido, demon magic as well as in the art of Konsō, the process by which a Shinigami sends wandering Pluses in the Human World to Soul Society if they are good in life, or Hell if their life was full of evil acts. You are also extremely long lived, with some of the captains having lived for 1000 years. You have knowledge equivalent to a freshly graduated Shinigami, and have the potential to reach the level of captains and beyond.
(You can customize your Shikai and Bankai ability. Also you can customize the general appearance and personality of your Zanpakutō.)