In Act 1: Beyond This World's Stars, when Lumine was leaving Liyue Harbor, she then sees Mona saying "Finally." Mona then came to Lumine and checked her with her astrology, and Paimon asked Mona if she is some door-to-door fortune teller and, if so, then they're not interested. Mona then tells Lumine that she isn't from this world (Teyvat). Mona introduces herself, and Mona wanted Lumine to be her disciple, but Lumine disagreed, so Mona told her she doesn't need to be her actual disciple, but she just needs to act like one. Lumine then agreed, and Mona told her that they're going to an inn before going to Mondstadt first. When going to the inn, a man named Mr. Zhu was seemingly stressed out due to his ring being lost. Mr. Zhu told that he was going to give mora as the compensation, so Mona then told Lumine to find the ring and give it back to Mr. Zhu.
After Lumine found the ring, she then gave it back to Mr. Zhu, Mr. Zhu gave the mora but Mona blocked both Lumine and Paimon upon getting the mora. Mona felt that she have indeed contributed upon getting the ring so Mona told Lumine that they will spend the mora on treating her a great meal. Mona tells Lumine not to thank her as she is just doing as a great master should. Lumine and Mona sat down in Wangshu Inn, while Lumine ordered Golden Shrimp Balls, Vegetarian Abalone, Crab Roe Tofu, and Salted Pork Soup. Mona seemingly asked the waiter how much does the current dishes costed, as which the waiter replied about 20,000 mora, which was also probably the same amount of the mora that Mr. Zhu had, so Mona had to order 1 dish. Lumine decided to cook more food for Mona, and when Lumine gave the food to Mona, she was amazed with the food that Lumine made and said that it was too delicious and that she have never eaten anything this good in her life.
When they arrived in front of Mondstadt, they then meet Klee as Mona told that Klee was the successor she was talking about. Lumine thought that it was some mistake. Klee ran to find the box that Mona was looking for, then Mona told Lumine to go with her. After retrieving the box, Mona was surprised that the box had nothing inside it, Mona told her she was looking for the stuff that was inside but Klee told her that it was the book in her hand. Mona was surprised about it, and Klee didn't knew what to do so she left while panicking. Mona then had to stay in Mondstadt temporarily so Lumine went the Katheryne upon asking if there is a house. Katheryne answered that there was a house concealed. Mona then was able to unconcealed the house and also rented it. Mona then thanked Lumine and wished her safe travels.
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Lumona's main rival ships are ScaraMona, which is Mona's most popular ship, and ChiLumi, being Lumine's most popular ship. In other cases Monaether can be but it doesn't really matter as all of Aether's and Lumine's ships are usually the same being the fact that only the player can choose who to pick. As of now, there is not that much content for Lumona since it's a small ship within the Genshin Impact fandom. Although, they do have some interactions together. On AO3, Lumona currently has 20+ works.