Bleach: Season 1, Episode 211

1 - 211: Betrayal! Aizen's Secret Maneuvers

Shinji's group manages to restrain Kensei using a powerful Kidou spell but then Hiyori also undergoes 'hollowfication'. They are then attacked by Tousen and as the rest of the group undergo 'hollowfication' Shinji battles against Aizen and is almost killed when Urahara and Tsukabishi arrive to save him.