I've watched quite a lot of anime over the past few years, but the only one that fills me with joy every single time I watch it is Lovely Muco (Itoshi no Muco in Japanese). It's about a Shiba Inu called Muco, who lives with her human Komatsu-san. Each episode has several short stories about their day to day lifes: going for walks, first snow, Muco's shiny nose, Muco's very shiny nose!
It's impossible to not fall in love with Muco's adoration of herself and Komatsu-san. Her number one dream is for Komatsu-san to finally turn into a dog so they can run and play together. It's so freakin cute!
And if you don't want to watch it for the cuteness, watch it for the life-lesson: Muco's relentless optimism, admiration of herself and ability to enjoy the little things in life can be quite inspiring! And it's also just really really cute.