Requirements japanese citizenship for a gaijin child born in Japan?

Hello everyone, I have a question regarding the japanese citizenship, maybe some of you were in a similar situation too.
My partner lives in Japan with her child, who was born there and has the filipino citizenship, due to both his parents having the filipino one. The kid speaks japanese fluently and is currently in kindergarden and will go to a japanese school too.
Is there a possibility to apply for the japanese citizenship for him and what are the requirements?

by ChaoticProton