This episode is mainly a flashback episode, revealing a lot about Momo Hinamori's past.
The episode begins with Momo inside her cell staring at the moon which causes her to reminisce about the past. It begins with showing Toshiro and momo when they were kids and lived in the same district, Momo tells him that she is now leaving to go to the Shinigame Academy, calling him "whitey Chan" which Toshiro responds too by spitting water mellon seeds at her, Toshiro doesnt seem to care much that shes leaving but that may be just his brattish personality showing as we know he cares a lot of Momo.
Their is then a time skip and we see various people in different classes such as Kira, Renji and Rukia. The class we mainly see is a class practicing Kido. Momo is called up along with other people, she actully managed to hit the target unlike the many other people who cant even reach the target, everyone is impressed at her talent for Kido, Then Kira steps up and gets a direct hit destroying the target, everyone is even more impressed, finally Renji takes his turn and blows himself up comically.
After this we see the three participate in a field training excercise against a fake hollow. The team quickly and easily dispatches the hollow, by working together. Suddenly everyone is attacked by a Giant Hollow, Hisagi demands that they all flee among all the other students which Renji and Kira start to do, Momo goes back to save Hisagi who is quickly getting overwhelmed, alredy losing sight in one eye. Renji and Kira go reluctantly to save momo and HIsagi. All three of them fire a Kido blast at the hollow slightly damaging it, they then take the chance to flee.
Unluckily they are then surrounded by a dozen giant hollows, as they are about to get killed, Aizen and Gin appear, destroying all the hollow with ease, he apolagises to Momo for being late and that they did well.
With that momo looks up at the moon which causes the time to switch back to the current timeline where momo is still staring at the moon, suddenly she approaches the guard of the cell and uses a Kido spell to knock him unconcious, the episode then ends.