Blade Below the Shoulder: Some types I and II exist; the former because a strap-on “weapon pod” is a standard accessory for quick-draw weapons, some of which might as well be blades, and the latter because – well, while they’re as impractical as concealed weapons as any other cybernetic implant, X-rays being a thing, and probably not the most useful thing you could stash inside your arm anyway, some people have funny tastes and like the notion of weapons attached to them.
Type III is certainly possible, but it not being considered an idiotic self-handicap probably isn’t. That discourages people.
Laser Blade: Dear gods, no.
Firstly and perhaps most importantly, light does not work that way. Most specifically, it does not stop.
Apart from that, you could try and fake it with a hot plasma bottle – if you want a melee weapon that sets everything around it, including you, on fire. And requires a ridiculous amount of power even by the standards of people who pack uranium-fluorine molten-salt reactors into power armor. And takes time to cut and so can’t be conveniently waved through solid objects. And has a hilarious vulnerability to magnets.
…and still doesn’t behave like a magical laser blade.
(There are both laser torches and plasma torches. They’re short-ranged industrial cutting tools, and mostly unsuitable for use as even improvised weapons unless you’re going all No Mister Bond I Expect You To Die cackle-cackle elaborate deathtrap for some reason.)
Like most ridiculously excessive weapons, the unique anti-materiel/area-denial weapon, “Sweet Kynthia”, was built to impress a lady, constructed by Sarai Iliastren-ith-Weváren during her pursuit of Kynthia Andracanth-ith-Andracanth, whose interests in heavy weapons – and indeed, whose own creations (see pps. 36, 42, 138, 196, 211, 335, 401, 545, 607-611, 720, 1196, and much of the rest of the book) in the field – have been proverbial.
Sweet Kynthia is an antimatter scattergun, firing two dozen individual coated one-gram antimatter pellets in a star-circle dispersal pattern – adjustable for wide or narrow scatter, each with an individual yield of 43 kilotons, the weapon’s total conversion yield being just over a megaton.
Given the multi-mile range of both the blast and thermal flash, and the mile-plus range of even the generally lethal prompt radiation pulse (rather less than the effective firing range), Sweet Kynthia has served primarily as a weapon of intimidation, given the essential impossibility of surviving firing the weapon – although it has been picked out of enough smoldering radioactive craters during its long and memorable career to lend the sight of it in a determined or desperate hand real weight.
– the Big Boys’ Book of Boom
Fellow Congregants, Cousins in the Army of Kalasané, Sword of Heaven:
By the word of the exarch of Kalasané the Ever-Victorious, We of the Prelacy are commanded to speak His displeasure.
Kindred, our eikone is the Laughing Warrior, a Lord of War. Remember that it is unfitting to stand in His presence, in the precincts of His temples, without being armed as for War. In earlier days, the sword and pistol you carry may have satisfied Him, but in these days in which they are the common arms of all daryteir, He requires more of you.
From this cycle forth, let none attend the Musters of Kalasané without at the least a weapon of the carbine class, and armor of the first military grade, or their equivalents; and know that further armament is apt and pleasing in His sight.
– Prelate Deximos, Fane of the Bound Axe
(Those cousins who require training or assistance in obtaining these weapons of war should consult Tetrarch Valeni of the Fane’s templars.)