Thanks for bumping or I would have missed this entirely.
I've been a fan of the original art series for a long time, and I'm actually kinda surprised I haven't seen a written adaptation like this before.
Very good stuff so far, and I'm looking forward to the possible continuation too!
Hm, as for execution ideas... how about some animal slaughter style ones like gutting/evisceration or a bolt stunner? Maybe being hung upside down and having the throat slit? I also support some previous suggestions like hanging and seppuku.