Visiting the Ice Thingdom is obviously always gonna tag at Simon's trauma.
And Ice Thing has got to be Complicated for him because he's both the person who loved Ice King the most and an incarnation of specifically the parts of Ice King people miss now that Simon is back. Basically just this cheerful happy-go-lucky silly Ice Wizard without the misery Simon was living through and the harm he was causing. And also Ice Thing does still sees Simon as Ice King on some level, since he's his 'daddy'.
So with all of that considered, and the fact that Simon is here to just Sacrifice Himself to Cursed Magic to Save a Loved One in a slightly different way than before...
The fact that he did find it within himself to smile is still very sweet, I think.













