He's being very agressive, which seem to be better than just getting more of them back(like Murray sometimes does), it unsettles Raonic a bit.
Well, I think that Murray`s tactic would work more often than Nishi`s. It`s harder to return Milos` bombs with agressive shots, surely, than just return ball in play. With Raonic, IMO, better get 6-7 point out of 10 in play somehow to have a chance get UE from him in future than 3-4 (out of 10) times hit the ball waiting for immediate point.
Though If Kei`s return is on fire, than yep, he is bigger threat in this department.