These are problematic at best.
I was examining a similar 'dirk' a few weeks ago and whilst beautifully made with a striking hamon, the overall feel didn't seem right for a wartime piece.
It also had the complete shark/ray skin cover, but I remember that the joins on the skin seemed slightly 'ragged' and ugly. I actually disassembled it and the tang seemed artificially aged.
I would be interested to see your piece taken apart if you don't mind?
The definately genuine examples are in my limited experience mounted in plain wood, or even more rarely leather covered. (sometimes in a linen or leather cover/bag).
The one's I've seen also have 'flush' collars and not the tapering ones that your's has.
So, as a background on these, they certainly DO exist, although for obvious reasons they are rather rare.
The 'Kamikaze' (Divine wind/God Wind) pilots were allowed to carry a small Aikuchi dagger to allow him to slit his jugular vein in the seconds before impact.
Clearly the practicality of being able to do this while under heavy fire from the ships and wresting with the controls to stay 'on target' is debatable at best and it's unlikely that many pilots managed to say a prayer and slit their own throats and still hit the target.
However, that hasn't lessened the 'legend' of the Kamikaze and the demand from collectors for their 'dirks'.
As with all 'suicide bombers' the psychological effect, fear and damage to morale that they engender in those on the recieving end cannot be underestimated.
Bearing that in mind it's easy to understand why the 'Kamikaze dirk' has always been a desirable and sought after item.
After the war, when Japan was occupied and awash with American servicemen looking for souvenirs, I've often wondered if some of these 'more elaborate' Aikuchi were produced as 'letter openers'
and sold to servicemen with a 'wink and a nudge' (or whatever the Japanese equivilent is).
That's just a thought, I have no evidence to back it up as I've never really attempted to look into it.
One thing is for sure. There are a lot of similar fakes that have come from China and continue to do so.
So! Is it a Kamikaze dirk?
I'd say not.
Could it be small non-military Aikuchi? You'll need to take pictures of it in pieces and wait for those who collect such things.
Or is it a later 'post war' souvenir?