1) It appears to be simply a thermo-labile toner in a modified laser printer.
2) The term"leuco," meaning white or colorless, is usually used to refer to the reduced form of the dye, as I mentioned with respect to methylene blue. However, it is not necessarily the reduced form.
3) As a wild guess, look up formazan chemistry. That group of compounds is unusual, almost unique, in that the leuco form is the more oxidized form.
4) The details are probably closely guarded by Toshiba. That process has had no impact in the USA. Bulk reprocessing of used paper is probably more cost effective and certainly much more secure than reprocessing single sheets, from which latent images might be recovered.
5) You might also be interested in the chemistry of Crayola magical markers that are invisible until developed.
Still, why are you interested in this arcane subject?
John