Alolan Raichu makes sense now.

Remember Puka from the anime?

>His eyes are blue, while Ash's Pikachu's eyes, as well as most Pikachu eyes, are dark brown.

Like Alolan Raichu

>Puka can sense big waves coming to the Seafoam Islands beach where he lives, causing his eyes to glow.

He's a surfer, he might also be based on the minigame of the Surfing Pikachu, located in Pokémon Yellow Version in Route 19, near Seafoam Islands.

What do you think about it?