The backstory of Shiba Isshin. After going through so many events, Ichigo finally gets a chance to slow down and listen to his father talk about the history of the Kurosaki family. Since time doesn't pass very quickly in the Bleach timeline, Ichigo never really questioned his past. For us viewers, though, we've definitely felt all along that there was a hidden secret in his history. 
Through the earlier Bleach anime, we knew that Ichigo’s mother died suddenly, which drastically changed his personality. Later on, we learned that Ichigo’s father was a Shinigami, which somewhat explained why Ichigo could become a Shinigami himself, but that still didn't fully explain his massive potential. Starting in Episode 11, we finally get a glimpse of what actually happened in the past. The love story between Shiba Isshin and Kurosaki Masaki. Although we've followed Ichigo’s journey for so long, we didn't really expect or guess that he had such a complicated past. Ichigo’s father is a Shinigami, but his mother actually came from a completely different world, she was a Quincy. Quincies and Shinigami shouldn't get too close since they share a brutal history, but Shiba Isshin and Kurosaki Masaki show us something different. Of course, Isshin knew what a Quincy was, and Masaki kind of understood what would happen when a Shinigami met a Quincy. Even though they knew the risks, Masaki was still honest and spoke the truth, and Isshin accepted everything she told him.