Throughout the Pokemon franchise, there has always been friendships between Pikachu and something, or a pokemon and something, whether it's love or friendship. So so far, what's your favourite pokemon pair for friendship?
My favourite one is Piplup and Pikachu, those two are cute together, and they were always shown to own great friendship. An evidence of this is the Japanese ending where Piplup had an argument, but they made up, it has to be one of my favourite ending of all times.
Other than that, Shellos and Piplup during one of the Galactic episodes was pretty cute.