These are some of the characters imo would lift your mood up by just looking at them or being with them.

If I Have to pick it might be Amber, she's literally the first one we meet and to help us out. She's like a ball of sunshine with how free spirited she is.

Yoimiya, since she has the most heartwarming smile imo. I love that birthday art

Bennett’s world is literally constantly trying to make him miserable but he still remains an absolute sweetheart!

Bennett's like the embodiment of perseverense and adventure spirit.

Very close between Mualani and Yoimiya... But I'll have to go with Yoimiya ultimately. The way she interacts with just about anyone, especially the kids! She's just a really relaxing character in general. Mualani is very close behind though, and then Amber.

I am biased against Benny.

They're all very positive and outgoing in their own way, but I have to go with Bennett because he has every reason to be completely miserable yet chooses not to, and that's the most powerful form of optimism imo