In "The Light of Dawn", Hollyleaf ran away from the tribe and entered the tunnel because she couldn't bear that she was a mixed-race cat, and lived with the ancient cat Luoye who was lost in the tunnel. In the tetralogy "Return of the Samurai", because he helped the lost Dovewing and Ivypool leave the tunnel, he was discovered by Lionblaze and brought back to the tribe.
Conception: