One heartwarming scene could be when Deku saves Uraraka from a difficult situation during a battle. He might use his newfound power in a creative way, and Uraraka looks at him with admiration. Another could be a moment where they study together and share their dreams and fears. They encourage each other to keep going, which shows the depth of their friendship and potential romantic relationship.
In some fanfictions, there's a scene where Uraraka gets injured and Deku stays by her side the whole time in the hospital. He brings her flowers and little gifts. He also tells her how important she is to him and the team. This kind of scene really shows their closeness and how much they care for one another.
A really sweet scene could be at a school dance. Deku nervously asks Uraraka to dance. They start off a bit clumsy but then get into the rhythm. As they dance, they have a conversation about their future. Uraraka mentions how she hopes they can always be together, whether it's as heroes or just as friends, and Deku blushes and agrees.