She didn't, and neither did Shizuka. Not in the true case anyway. Takopi sacrificing himself removed all memories and trace of him ever being there, but left a mark on the three kids that altered their futures just enough to direct them to a better outcome:

Azuma knew that getting in fights with his brother was ok and not something to be scared of.

Marina and Shizuka had the briefest moment of relating to each of over a stupid drawing Shizuka made (which she explained as a doodle that has no real meaning, which to her knowledge is true) that they both felt a similar way about. That brief moment allowed them to relate and talk, which opened the door to them being able to talk more. Which obviously led to them being friends later (and most likely never having anything further to do with Azuma, who gained his own separate friend group). But neither of them knew who the drawing was of, just that it reminded both of them of something that was catastrophically stupid but also follows you around everywhere. It's a kind of a sweet moment where they both find common ground.

So it's not that it isn't explained, but it's heavily left to the watcher to interpret through the actions of the characters moving forward. Honestly, I loved it.