In Mondstadt's Quest, Act 1: The Outlander Who Caught The Wind. Lumine first meets Kaeya after Dvalin being defeated by Lumine and flying off to the unknown, Kaeya was seen clapping as he says she actually has the power to go against Dvalin, Kaeya asks her if she is a new ally or a new storm. Amber introduces Kaeya to Lumine, Kaeya welcomes Lumine to Mondstadt, Kaeya then says that he understands the anguish of being separated from her family. Kaeya brings Lumine to the headquarters.
While helping the Knights Of Favonius, Lumine sees Kaeya and the both of them decided cleared out the Temple Of The Wolf. When they did cleared it out, Kaeya then clapped and said "Bravo! What a perfomance". Kaeya tells to Lumine that she are, to his surprise, a well-trained knight.
In Mondstadt's Quest, Act 3: Song of The Dragon and Freedom. After Lumine defeated Dvalin, Lumine then meets Kaeya again, Kaeya tells Lumine that her great battle sharpened not only her combat skills, but her wit as well. Kaeya tells Lumine about the Abyss Order. After talking about the Abyss Order, Kaeya had to leave.
In Act 1: Secret Pirate Treasure, Lumine meets Kaeya at the headquarters, she sees Kaeya seemingly worried about something. Kaeya tells Lumine that he cannot seek any help from anyone else but her. The both moved to the courtyard just outside of the headquarters to talk. Kaeya tells Lumine one of his secret and it was a secret from his past, and he'll confide in her to keep it. Kaeya tells that there is a treasure somewhere, so Lumine then helped Kaeya to get the magical sword since Kaeya said that the treasure was a magical sword fallen from Celestia. While Lumine found nothing as she went back to Kaeya, Kaeya then gave her some clues and tells her that she'll be compensated for her troubles by Knights. When Kaeya said that there was no treasure, Kaeya then gave Lumine a Harbinger of Dawn sword to repay them and asking for forgiveness.
In Act 2: Current Deep Beneath the Lantern, Lumine meets Kaeya again. Lumine then relates what she had seen to Kaeya, Kaeya then tell Lumine something. "Wine begets wisdom.". Making Lumine tell the informant "Wine begets wisdom.". When coming over Windrise to see Kaeya's informant.
In Act 1: Ode to Flower and Cloud, after Lumine giving people some advice, she meets Kaeya. Paimon didn't knew that Kaeya would wanna learn how to compose love poems, too. Lumine thought that Kaeya wouldn't need any help in that department.
In Act 2: Missive of Cloud and Fog, Lumine meets Kaeya in Jean's Office. Kaeya tells Lumine that she was just thinking about her and Paimon. Kaeya asked Lumine a flavor, Kaeya tells that he has a drinking buddy that wants him to help with something but since Kaeya is too busy, Kaeya then asks if he can entrust the matter to her.
Most of the ships that includes Aether and Lumine, they tend to be controversial within the fandom as their looks of being a minor. The both have lots of interactions of each other so KaeLumi then became a semi-popular ship. KaeLumi currently has about 115 fanfictions on AO3.