Chat Noir or Ladybug gets sl injured during one of their fights so the other takes them somewhere safe to get him/her treated. Ladybug tells of Master Fu's shop, so the two heads to the shop. But once they arrive, they de-transform, revealing their identities.
After Master Fu treats them and introduces himself to Adrien, he gives them some privacy. The two then engage in a conversation along with their Kiwami friends. They reveal to each other their struggles, past conflicts and....true feelings about each other (along with hearing words of encouragement from Tikki and Plagg)...then they kiss.
After that, their bond is stronger and their new relationship begins as Master Fu comes in, asking them if they want to stay for tea.