After Mario and Peach break up once again, Luigi reveals that he longs for a girlfriend of his own. Jack Skellington pops up to recommend Luigi an app called Tinder. After a few unsuccessful candidates, Luigi enthusiastically chooses Daisy to be his girlfriend. Mario comes along with Luigi the next day to help Luigi out on making Daisy fall in love with him. He gets the idea to write a love song to Daisy, which works wonderfully and the two start their relationship in harmony. Meanwhile, Mario tries to get Peach back to his side again (despite muttering to himself his hatred for her, though he loves her "tush") by writing a love song to her, which sounds insanely bad when he plays it to Luigi.
It's not long though till Daisy starts to become very overbearing to Luigi to the point that he would decide to break free from her obsessiveness towards him. He announces the breakup to Daisy, who doesn't take it too well. She ties him up, and bullies him into writing another love song for her. Despite his refusal, Daisy picks up a hammer and breaks Luigi's legs with it. Luigi then remembers Mario's terrible love song, and plays it to Daisy. The song disturbs her so much that she goes out to the porch and jumps off it.
In a post-credits scene, Peach announces to Mario through speakerphone that she's leaving with Daisy to start a new life in Las Vegas.