Why does Tokyo Ghoul √A tell a different story?
Tokyo Ghoul √A (“Root A”), Studio Pierrot’s second season, aired from January 9 to March 27, 2015, in twelve episodes. It was conceived as a departure from the manga: the production asked Sui Ishida to write an original draft for the season to work from. In a later interview, Ishida indicated that his version of the draft was not used. The reason has never been made public.
What aired instead is best described factually: a condensed version of the manga’s second half with anime-original turns, the largest being that Kaneki, who in the manga forms his own group against the Aogiri Tree, in √A joins Aogiri. The sequel anime, Tokyo Ghoul:re (2018), then adapts the :re manga directly, which is why viewers who follow only the anime meet a story whose middle took a different road.