It’s still a weird title in English, though. It’s not clear (to me, anyway—there’s always the possibility of a complex Japanese pun lurking somewhere) why the MC, or any of the characters, would be analogous to that specific type of flower.
Welp a quick Wikipedia search did not make me happy
“In other cultures, the meanings differ. In Chinese and Egyptian cultures, the flower of anemone was considered a symbol of illness due to its coloring. The anemone can be a symbol of bad luck in Eastern cultures. The Japanese anemone may be associated with ill tidings.”
Just from what we've seen so far, "symbol of bad luck" might be an angle worth exploring. At the beginning of the story, they're both suffering from what they see as bad luck - Nagisa not getting the school she wanted because she simply took the time to help a random stranger, and Mashiro back in the infirmary again no matter how tired she gets of the place. But without those things happening, they wouldn't have been able to develop this warm relationship together.
Of course, that's mere speculation based only on the chapters I've seen so far. Maybe future developments will cast the title in a new light.