As long as one has the intelligence and mobility of a child about seven or eight years old, it will do.
The only thing required to cultivate it is life span!
But what has this got to do with the host? The one who cultivates the Dark Demon's Hand is the Shadow Demon, and the one whose life force is sucked out is also the Shadow Demon. Dark creatures have immortality and ridiculously long lifespans. Isn't it a perfect match to let them practice the Dark Demon's Hand? It's as though they were made for each other.
Anyhow, you can kill them in training, and the host doesn't feel any pity.
When the Dark Demon's Hand becomes powerful, the host's disadvantage of controlling the dull and clumsy Shadow Demon can be resolved. Because the Dark Demon's Hand combat style doesn't require much flexibility, all I need to guarantee is that the hands can touch the enemy and absorb their vitality!
The pair of arms that the Shadow Demon possesses are indeed extraordinarily gifted.
