The Plasma Laser, sometimes referred to as the "Toothpaste" Laser, is a primary weapon first introduced in Raiden II. It is a purple laser beam that locks onto nearby enemies, causing it to bend and flex just like toothpaste. It can be acquired by collecting a purple power-up.
The Plasma Laser first appears in Raiden II as the newest primary weapon the Raiden crafts are capable of utilizing, upon acquisition by the Raiden mk-II, will initially fire fast bullets similar to the Vulcan Cannon, only with a purple tint. They will gradually fire at a faster rate until they eventually form a thin, purple beam of plasma that will attach itself to the nearest enemy and drain the health from them. It proves to be quite useful against the smaller enemies, but less effective on larger ones.
In Raiden III, the Plasma laser is replaced by an alternative form called the Proton Laser, which differentiates from the Raiden II variation by stretching out a attacking nearby enemies in a similar behavior to tentacles of cephalopods (octopi and squids). The form of the laser also contrasts to the original Raiden II version as it has a thin green outline to it rather than a full-on purple appearance.
The original Raiden II version, along with a more modified version of its successor, return in Raiden IV, with the former being largely uncharged save for an update to make it appear more three-dimensional.
In combat, the Plasma Laser proves to have better accuracy and range than either the Vulcan Cannon or the Ion Laser. Because of these perks, the laser is a great choice for destroying large groups of smaller enemies, it will simply sap the health straight out of them in just mere seconds.
On the downside, the damage output is below that of both the cannon and the Ion laser, as when used against the larger enemy units such as bosses, it takes notably longer to destroy them. The low damage can most likely be seen as a counter-balance to the high accuracy of the weapon. In addition to the low damage output, there is a start-up delay for the actual weapon when initially acquired by the player, as it will originally take on the appearance of the Vulcan Cannon, this property also occurs when switching to another weapon then switching back to the laser.
To counter the low damage output, the player must regularly acquire purple power-ups to upgrade the weapon, in doing so, they will increase the thickness and damage output of the beam.