I don't understand why people are complaining about this arc.
When we got a comedy and wholesome chapter people are complaining because it doesn't move the plot.
And now this arc Hata-sensei significantly push the plot forward and people are still complaining about Tsukasa character being ruined.
No! Her character is not ruined! She is a really deep and delicate character. She literally lived for thousand of years alone she even forgot her real name. And about the promise, her whole relationship with Nasa and why she marry Nasa is based on his promise. Of course she would be afraid after she found out Nasa forgot his promise. She may went too far by asking a divorce, but we should be able to understand her after all she went through. Nasa know about this and that's why he didn't want to face Tsukasa before remembering because he know Tsukasa would do this.