If you liked
Steins;Gate Movie: Fuka Ryouiki no Déjà vu
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...then you might like
Seishun Buta Yarou wa Randoseru Girl no Yume wo Minai
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In both of these movies, the male protagonist gets forgotten by the world due to their inner difficulties in accepting their current state of the world. They are however ed only by the female protagonist who tries to save them from "disappearing".