This is a death caused by use of the quirk the user has.

As a result, the quirk starts to power the body, taking energy from any food eaten.
The only signs of this is the lack of a heart beat, possible numbness, and any physical changes to channel the quirk better.

The body simulates being alive (moving chest, swallowing etc.), so it is difficult to catch this in individuals who have experienced a quirk death. When found out they will most likely try to play it off to not cause panic.

Those effected by this die when they are destined to, the quirk is a sort of ticket to life until the person must die.