Undo is a purely artistic film. It is about a visual representation of a psychiatric disorder.
Although as a movie, the narrative structure, the lack of dialogues and relevant scenes to give us more context needed of the story, the film is a unique sensory experience to watch !! The directing is absolutely stunning.
It is pure visual art, more than a film.

Moemi and Yukio are long time lovers, but their relationship is fading away. They love each other but aren't in love anymore.
Moemi is trying to change things to fix their relationship but Yukio is uanble to express what he really feels. She is willing to stop her own evolution just for the sake of Moemi being able to see in Yukio what made him in love ... (her choosing to put back her braces because he was used to them)
"You don't like it?"
Moemi's insanity starts. She has this compulsive need to attach things to her, so that they don't leave her. And in the movie, I feel like it started when Moemi asked Yukio why their kiss didn't feel as good as before (but she felt it too, she knows when she kisses him, the intense feelings aren't there for her too) .
He couldn't really answer, he couldn't give an answer, simply because he really didn't know why his love had changed, she started to brush his hair, her hands yearned for his hair, as if she wanted to hold them, because indeed both were noticing how far they were drifting away.
The braces were just a symbol of it, and now knoting things is the only way she finds to cope with the traumatic revelation that their love is dying by itself, with no actual real reason than the simple exhaustion of romantic feelings.
An ‘Obsessive Knot-Binding Syndrome’.