If I remember correctly, you have to finish the Priest's Angel Statue Quest. You get that quest after you complete Undercover Mission II with the police officers.
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Thank you, it worked! I finally proposed! Since you're so reliable, do you know if you can win the cooking contest the first year? I had my cooking skill all the way to Master and even read all the cooking books, as well as the recipe on the bulletin board, but MC still said he's not skilled enough and hasn't finished it as a result, and lost. Also, do you know if the God of Love Quest will be important to the story like the cops and church quests? Because my game glitched that I can't get the general store magical ponpon figurine. Will you need to complete his quest to progress the story at some point?