The system for capital punishment in Japan is "wacky" (in an unfunny way). The execution times are kept secret - even from the convicted who must wake up every day wondering if this is the day. The executions are announced *after* the fact. Given the recent cracks in their own system of obtaining convictions (interrogation processes), a review is the least I'd recommend.
Just from a medical standpoint - hanging, if computed properly, is just about as instantaneous as any form of killing.
As to the morality of capital punishment -- thats its own whole thread but my main beef with it (at least in the US) is that the justice system has gotten the *wrong* guy so many times as we've discovered through DNA testing that execution loses its merit simply on that basis. Frankly, true life imprisonment with required daily reflection on the crimes that sent you there is a much better form of hell to me
but it also permits the possibility of mitigating mistakes made by the system.