Grounding the story in the here and now, Harley’s youth and skills help Tony Stark in his darkest hour, and help him survive in a mostly suitless portion of his adventure. He has to rely on his brains, as well as his willingness to work with a teammate, and in the end Tony rewards Harley for his efforts with a tricked-out lab. While he didn’t know it at that time, Harley Keener’s gratitude for their time together in Iron Man 3 was something so strong, he’d eventually show up to Tony’s funeral in Avengers: Endgame.