Fangraphs had him at a Scout - of 89 (100 is average, lower is better, just like FIP -) in the Puerto Rican Winter League through 5 starts. In 6 starts, he has a 4.736 FIP, with a 4/1 K/BB and 1.08 GO/AO but a high home run rate. Against right-handers, he has a 16/1 K/BB, but 4 homers in 15.2 innings. From what I can see, league average HR/9IP is just .61. Obviously small sample size applies and Kasahara is younger than his competition, but he is still struggling with homers nonetheless.
The right-handed pitcher has good size at 6-3 210 with a high leg kick and quite a dramatic pause in his delivery. He has a strange leg drag in his delivery where his body is almost already lunged forward before his leg actually strides. Eventually, this causes his body to get pretty low before delivery the ball (something I have seen in a few Dominican native pitchers, though the pause and leg kick is Asian baseball in nature).
According to his NPB tracker data, he has 7 different pitches, but his fastball is just 86 MPH (according to this video, he has hit nearly 90 MPH). He throws a "shutto" (2-seamer basically) and a sinker, along with a slow 70 MPH curve, very soft slider (74 MPH), a change and forkball.
I had a hard time telling the difference between the moving fastball, the 4-seamer, and the sinker. Velocity and placement is mainly what I would go on, because I didn't see a big difference in movement. He would throw some down in the zone with a little bit of movement with the velocity of a 4-seamer.
In video I saw of him, he seemed to like his slider, but he couldn't really get it down. It broke like what is usually described as sort of a "baby slider". His curve breaks the same way, vertically not horizontally, but is more dramatic, and obviously, slower. The pitch gets down to 67.5 MPH.
Despite his great selection of pitches, his favorite pitch still seems to be the high fastball. Kasahara seems to work high then low (or vise versa) about as well as you are going to see any pitcher. He seems to be able to run his fastball into lefties (it doesn't move quite like a cutter, though perhaps you could call it one just on movement).
Obviously the fastball velocity limits what Kasahara can be, but the selection of pitches is, at the very least, interesting. You always wonder about pitchers with this many pitches, as to whether or not they have too many "tools in the toolbox". If he can use them right and limit walks (and repeat his delivery, which is a feat in itself), he won't be overpowering, but he may develop into a decent NPB pitcher by keeping hitters off balance. Because even the breaking pitches aren't spectacular, I don't think he is a guy who could come to the MLB and have real success.