Use Ichigo or Bankai Ichigo.
Use Urahana.
Use Hinamori.
Play Soul Road (Hard or Normal) and answer the question correctly, which the answer will be the name of the character you will unlock. The question will only appear when you hit on the blue spot with at least 60\% Trust or more.
Use Renji or Bankai Renji.
Use Ishida or Final State Quincy Ishida.
To unlock this rather special mode, simply beat all 20 missions (under Mission Battle > Story Mission)
Use Chad.
Win 10 or more battles in Survival Mode to unlock EX Survival Mode. It can be done with any character, and whenever you want.
Use Yoruichi.
Use Kenpachi.
Use Gin.
Use Rukia or Shinigami Rukia.
Use Rangiku.