WARNING: The following contains spoilers for Episode 10 of SSSS.Dynazenon, "Which Memories Do You Regret?," now streaming on Funimation. It also contains discussion of suicide.
When a time-bending, mind-controlling kaiju traps the Dynazenon pilots within their most painful memories in Episode 10 of SSSS.Dynazenon, it’s up to Yomogi to rescue them all. However, as difficult as it is, the trip to the past does offer value for at least one pilot: Yume finally gets the closure she needs when she is faced with the ambiguity of her sister Kano’s death.
The new kaiju is discovered by the Kaiju Eugenicists at the top of the episode. When Mujina attempts to control it, she vanishes, and soon the other Eugenicists disappear, too, not to mention many civilians along with them. It's then revealed that the affected people are trapped inside the kaiju wherein each faces traumatic experiences from their past.
Yume is the first to go from Dynazenon, and she returns to her childhood where Kano is still alive and still jaded towards her family. The others soon follow after and have to navigate their own past trauma. Yomogi is the first to break free from the illusion: His trauma involves his mother telling him about her new partner. But he is quick to remember his bond with Dynazenon and the other pilots, leading to his traumatic experience failing quicker in comparison to the others.
He then makes a valiant effort to break the others out from their memories, desperately trying to reach Yume, specifically, and eventually succeeding. Knowing that Kano will soon fall from the tower at the floodgate, both Yomogi and Yume rush in an attempt to stop her.
When Yume calls out to Kano, she has one foot up on the ledge but soon after Yume’s plea, Kano tells Yume that she wouldn’t kill herself or break her promise about the recital. Kano’s death seems to have been an accident, and, in her confusion, Yume realizes her true feelings: It doesn’t matter if the death was an accident or not. Kano’s death has a significant impact on Yume regardless. Yume wanted to spend more time with her sister, which is why she obsesses over the key details of the mystery.
As Yomogi runs off to free the other pilots, Yume finally takes the time to know her sister better. The following conversation reveals that Kano routinely used the floodgate as an area to practice her singing. Kano also talks about pushing Yume away due to envy. Yume’s agreeable nature made Kano want to reinvent herself in high school. However, Kano was unable to rely on others like Futaba, her ex-boyfriend.
Kano’s death in SSSS.Dynazenon can still left be open to interpretation, assuming the kaiju’s illusion isn’t an exact replica of the real world. Even so, Yume talking to Kano about why they didn’t get along, whether real or not, allows her to let go of her grief. In many ways, Kano wanted to be more like Yume when she was young and happy. Meanwhile, Yume looked up to Kano and wanted to be closer. The tragic story's resolution, at last, will no doubt contribute to Yume’s character arc going forward.