If someone told you that you could have any anime ability, would you pick the coolest single power that you could think of? Or would you pick a power that is the anime equivalent of wishing for more wishes, the ability to take on other people's powers as your own? Though rare compared to fire wielders or ice warriors, anime characters with power absorption abilities are some of the toughest fighters out there.
Exactly how this ability works varies from person to person - it can be as absurdly complex as Chrollo Lucifer's multi-step Nen attack, or as simple as a plant Pokémon's Giga Drain. It can have serious side effects like memory loss, as it does for Yu Otosaka, or it can have seemingly no drawbacks, as in the case of All For One. Sometimes, anime characters who can steal power don't have the inborn ability to do so, but go out of their way to take from others, as is the case with Danzo Shimura.
This is one of the most versatile abilities in all of anime - but because it leaves its victims without their power or even without their life, it's also one of the most cruel.