Ultimately, this will not impact the Normal Ending. It's up to the player if they want to keep romancing the same girl throughout Act 1, or try someone else. Another way to find out is to share the poem with Monika, after which she will mention the name of the girl who will like the poem best. And of course, the girl who loves the poem will sing it praises. This is one way to know which girl appreciates their poem the most. The next day, the player will have a moment with the girl they dedicated the poem to - even before the poem-sharing starts.
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The protagonist is initially reluctant to join, but after some convincing, they give in. After learning a little about each member's personality and preferences, the player must then write a poem to impress the girl they want to be with, by choosing their preferred words as listed below. The one exception is Monika. Sayori drags the player to the Literature Club, where they meet the other three members: Yuri, Natsuki, and Monika.