It’s Cardcaptor Sakura episode 27, and Sakura is taken back to the past by a new Clow Card, where she sees what happened between Toya and Ms. Mizuki.
Sakura has the dream she had before she found the Clow Book and when Shaoran arrived, except this time it appears to have someone who appears to be Ms. Mizuki in it. This wakes Sakura up, and as it’s still early, she goes off for a stroll, only to find herself at the Tsukimine shrine. She finds Ms. Mizuki, who is a maiden at the shrine, there and decides to help out. That night, Fujitaka sees that Ms. Mizuki is Sakura’s new math teacher, and tells her that she was a student teacher when Toya was in junior high.
Later that night, Kero feels the presence of a Clow Card and brings Sakura to the shrine, where they once again run into Shaoran. However, once they enter the shrine, they lose the card’s presence. There, Sakura and Shaoran have another argument over Ms. Mizuki, with Shaoran saying that he still gets an ominous feeling from here, while Sakura feels all dazed. Then the issue of Yukito comes up, and they both find out that it was “love at first sight” with him.
Shaoran gets embarrassed and runs away, but once he does, the card, which was hiding in the tree they were sitting next to, grabs Sakura and brings her into the tree. Kero then realizes that it is the Return card. Sakura finds herself next to the tree, but in a different time, where she sees the junior high-aged Toya on the day they moved to the town, where he also meets Ms. Mizuki for the first time.
Meanwhile, Shaoran and Kero wonder what’s going on, and Kero hypothesizes that the tree has it’s own magical powers, that Return is borrowing, but it could only send one person back. Sakura continues to watch visions of Toya and Mizuki, including when Mizuki tells Toya that she’s going away for studies overseas, and where we see that they had some kind of relationship.
Sakura then is drawn back to the present time, where she seals the Return card. However, it flies to Shaoran, who was able to bring Sakura back to the present by using the Time card. After all of this, the full moon reminds Kero of someone: Yue.
So we get more background information on the background between Toya and Ms. Mizuki, though it ends up being one of those scandalous adult student teacher/15 year old junior high boy relationship things, though we don’t really see how advanced the relationship is, only that they had feelings for each other.
We also see the first time that Sakura is really hesitant about bringing Tomoyo along, having decided not to after Tomoyo got trapped in Maze with her the last time.
Meanwhile, Kero mentions yet someone else new: Yue. However, who or what this might be, we have no clue yet, but apparently it has something to do with the moon.