The path of the laser is affected by user input and enemies present on the screen. Here is a video, at 5:00 minutes the laser in question is shown : Raiden II (PS) - 1 Loop Clear - Part 2

UPDATE

Here is a test using Inkscape, ship is at bottom, the first 4 enemies are targeted by the plasma. There seems to be a sort of pattern. I moved the ship first, then the handle from it to form a 45° angle, then while trying to fit the curve I found there are series of 2 parallel handles.

Another version with better aligned angles (now enemy 5 is aligned)