Hakugei is a theoretically possible ball - its a basically a backspin ball - which causes the ball to rise and hop and because of its extreme backspin - it flies back at fuji.
Well its definetly possible to create the hop effect in golf - because of the prolonged distance - i've done it before - but it requires the right equipment and alot of experience.
The flying back part is a bit extreme but its theoretically possible - of course humans would not be able to do this.
So aside from critizing the phyiscs aspect of this move - because it is at least theoretically possible.
When the hakugei flies back into fuji's hand - doesn't this actually count as the opponent's point. Its just like when if you hit the opponent in the body but it bounces back into your court - it is still the opponent's point. Also if you hit the top of the net and it bounces into your side.
I am just a casual tennis player so correct me if i am wrong - but wouldn't it make more sense for the hakugei to fly into the net on the opponent's side instead of fuji's hand?