Zephels background...lesse...parents died by hollows when baby. taken in by other quincies. Shinigami exile lived nearby and he used to practice with him until he discovered the man had been exiled for calling Soul Society on how they whole sale slaughtered quincy, or allowed it to happen.
Told adoptee's about it who killed old shinigami in his sleep. After he came to the home the next day and found the man dead by the mysterious unfound bullet he knew what happened, went home. Crushed up frig loads of hollow bait while a maid watched him crushing smarties candies, and when the hollows came he showed he wanted to join them by helping massacre his adoptive family.
From there he went with the hollows and presto chango, tainted ass quincy.
(never worked out how he was able to go to hueco mundo..but.....whatever.)