In the movie as well as the manga, when Hiyori disappears everyone forgets about her. But Tomoki still remembers about her. He gets a headache, but he still remembers her. And then everyone else starts to remember Hiyori too.
How does that work?
In the movie as well as the manga, when Hiyori disappears everyone forgets about her. But Tomoki still remembers about her. He gets a headache, but he still remembers her. And then everyone else starts to remember Hiyori too.
How does that work?
I'm pretty sure this is just another one of those cases where everyone was supposed to forget a certain character (Hiyori), but because someone (Tomoki) cared for them so much they were not fully affected.
The headaches are because he is not supposed to remember, but he remembers something. And because he remembers, everyone else does too.
So simply said he didn't forget because he cared too much. (Which makes it sound as though everyone else didn't care enough, but that's simply how these things work. The main character has to be the special chosen one.)
First thing similar I can think of would be Time Stranger Kyoko.
Kyoko is erased from everyone's memories and it is like she never existed. But after her bodyguard and lover finds a photograph of her he remembers and gets everyone else to remember her too.