What skill gives Demon Slayers their instant kill chance? Is it just something that comes naturally to them? I feel like that is the key to being able to train on monsters so much higher of a level than you. I was getting over 600%/hr at level 63 training in C-2 in Magatia on my 100% unfunded Demon Slayer using nothing but Silent Crusade 1000HP Potions. The trend seemed to work perfectly so that every time I'd use a Dark Thrust + Lash combo, at least 2-3 of the monsters would die despite having over half of their HP remaining. I do not hack, frankly I wouldn't even know how to, so that is obviously out of the question. I guess here's where I'm going with this...

1. What gives Demon Slayers their insta-kill ability?
2. Is the whole "being easily able to train on monsters 25 levels higher than you" thing normal throughout a Demon Slayer's life? Like...when I'm level 93, will Kentasaurus in Leafre be an option? LOL
3. Who else experiences this with their DS?