I still love the part of the Thalassophobia sequence where Mari's spirit stops, moves a few steps closer to Sunny, Sunny moves a little closer to her, and then they keep going. It's so cute and sad at almost any angle you look at it with.
And also this detail from the manga. That the first thing Sunny did after opening his eyes and seeing Mari crying was to try and wipe her tears. It feels so Sunny.