The prequel series Tokyo Ghoul: JACK follows the youths of Kishou Arima and Taishi Fura, two characters from the main series who become acquainted when they join forces to investigate the death of Taishi's friend by the hands of a ghoul, leading to Taishi eventually following Arima's path and joining the CCG (Commission of Counter Ghoul), the federal agency tasked into dealing with crimes related to ghouls as well.
The sequel series Tokyo Ghoul:re follows an amnesiac Kaneki under the new identity of Haise Sasaki, the leader of a special team of CCG investigators called "Quinx Squad", that underwent a similar procedure as his, allowing them to obtain the special abilities of Ghouls in order to fight them, but still being able to live as normal humans.