Initiative . not just roshi but all ninja with higher Ini will attack first

Roshi is almost always placed in position 1 by the player because they want him to take hits.

But the only reason he goes faster than your position 1 is because of the initiative stat of the player, Roshi is irrelevant.

He can be outsped, as I've seen mine outsped....a lot.

But, basically, it's mainly due to most Roshi users having loads of initiative, he's in the front to, which is a big factor