I've watched 16 episodes and the phrase "Zawsze in Love" (first said by Kirisaki) appears to be memorable both for her and Ichijou. But what does it mean? Is it a reference to something? Or is it another thing from their childhood?
"Zawsze" is Polish for "always."
So it's something along the lines of "always in love." The significance has yet to be revealed.
The original version is written as ザクシャ イン ラブ （愛を永遠に)
Which means more or less "forever in love."