Q. Is Hayabusa single seater? Can we add extra seat?

Actually, there is. The rear part for adding the seat (which is sold with the bike as an accessory) is covered by a seat cowl (the bump that can be seen on the pillion seat's place) which can be removed before adding the seat. All you have to do to replace them is to open two nuts that hold them. There is also an option for a pillion grab rail behind the pillion seat(again, sold with the bike itself).

It's 2 seater bike they ll giv you pillon seat too n it's is removeable

Hayabusa is best bike and fastest bike in world