who were the lead characters of this show?
Each episode has different characters . Only Reece cShearsmith and Steve Pemberton appears in almost all the episodes.
Inside No. 9
Each 30-minute episode is a self-contained story with new characters and a new setting, and all star at least one (usually both) of Pemberton and Shearsmith. 
inside no 9 season 1 episode 4 cast UNANSWERABLE when did this show first air? 2014. the show was written by whom? Reece Shearsmith and Steve Pemberton. what is the television show about? It is an anthology series, with each episode featuring a new story, with a new setting and new characters. It address dark topics like incest, child sexual abuse and murder. what is its genre? Black comedy anthology.
wiki:7641801
Inside No. 9 [SEP] Introduction
Inside No. 9 is a British black comedy anthology television programme that first aired in 2014. It is written by Reece Shearsmith and Steve Pemberton and produced by the BBC. Each 30-minute episode is a self-contained story with new characters and a new setting, and all star at least one (usually both) of Pemberton and Shearsmith. Aside from the writers, each episode has a new cast, allowing "Inside No. 9" to attract a number of well-known actors. The stories are linked only by the number 9 in some way and a brass hare statue that is in the background of all episodes.