Chillin’ Island
Super dumb and non consequential but goddamn if its not mellowing. Perfect show for any kind of burnout or blahs
Not sure if anime fits your bill here but Mushi-shi is incredibly relaxing and even though i don’t really watch anime anymore it still jumps out to me when i think of chill/mellow/relaxing. Traveler investigating forest spirits and whatnot, soft Japanese music score, taps hard into those nature vibes, more of a rainy day relaxing though not really happy-chill.