Cousin refers to female relative sharing common ancestor but not sibling. Sister is female sibling sharing same parents. Cousins can be first, second, or more distant relatives. Sisters can be biological, half-siblings, or step-siblings
Kuzen emerged in mid-Heian period as informal official document. Used by shikiji at kurodo dokoro to transcribe emperor's edicts. Initially conveyed verbally to shokei at Daijokan
Real name is Kuzen, former janitor who became a ghoul. Created the Aogiri Tree and was the SSS Rate's Undying Owl. Had a tragic past with his human wife Ukina. Created his own child, Chuckan's Owl, to protect him