" A Hollow is a ‘fallen’ soul, souls that weren’t brought to Soul Society by a Shinigami, souls that escaped, souls that weren’t protected from Hollows. The soul degeneartes, loses its heart and becomes a Hollow. To fill its empty heart, it seeks out those it loved most in its past life.” - Rukia Kuchiki "

― Tite Kubo , Bleach, Vol. 1 (Bleach, #1)