@Tersione
It's better if I imagine that the narrator is her improved future self looking back at the past.
I say it's her future husband, who, after witnessing his wife fall into a coma from an unspecified trigger, makes a deal with a higher being of power to go through Itai-san's memories on order to wake her up again.
This explains the surprise from the Narrator, since if this was her future self, she would already know what happened in her past and wouldn't be surprised (i.e. lying about having a boyfriend).