If you think you can just use the demo from your familiar PSN Store, then please read on to know why this won’t work…
As it has been the case since many many years, you are required to buy (in this case free of charge) an exploit game to hack your PSP (used to be the case) or PS Vita (still the case).
The exploit game had to be a Playstation Portable game, and so far nothing has changed about this.
While it is correct that there is a Toukiden Kiwami demo in the western PSN stores, it happens to be a PS Vita demo version, opposed to a PSP demo version.
Since you are required to have the PSP demo version for the VHBL, you are not able to use the demo from your familiar (presumable western) PSN store to exploit the game and run the VHBL on your device.
It seems that the Japanese PSN Store had been the only one which offered a PSP demo of Toukiden Kiwami, until now.
The demo got removed from the Playstation Store, and if you did not add it to your download list & download it onto your PS Vita, well then you are too late.
Like usually, you are unable to purchase the free demo, and you should be unable to re-download it as well (this varies from pull to pull).
But fret not, because the next VHBL release might come sooner than you think.