This is a collaboration between Pikachu and Pikotaro, called 'Pika to Piko'.  

In Japanese, 'to' (と) means 'and'. 

They released this new song on 31st August, 2020. 

Here is an article about the collaboration:

https://soranews24.com/2020/08/25/pen-pikachu-apple-pen-pokemon-star-teams-up-with-ppap-singer-for-new-song/