When doing a slash with the trait, it will take x amount of time before the trait is ready to be used again. If you input the trait grab (db4 or d4) after a cancelable normal so that it is trying to come out (you have just buffered it or you input it frame perfect) on the 1st frame after trait has recovered from the slash, it will come out as a cancel. With slash-f2 xx trait grab, the timing looks something like this: slash (wait 0.1 sec) f2 xx db4 (as fast as possible).
Timing is different for different strings and normals. b1 xx trait grab is like this: slash (wait 0.3 sec) b1 xx db4 (as fast as possible). With strings you have to do something like this: slash->2 (hit 4 with one finger, then 2 as fast as u can after with another finger) 13 (this should follow as fast as possible too) db4 (as fast as possible too). The 213 part will take a while to complete, but as long as you input trait grab early it will still come out after the string.
Good stuff!