What if it is the actual wish of the people involved?
What if a person whose fantasy was to kill and cook another person met a person who fantasy was to be killed and cooked? Then this happened. What penalty should ensue for the (well-fed) survivor?
Well, I'm controversial with some - it's still against the law in many jurisdictions so it's murder. But I consider euthanasia to be hugely unethical, so I'd consider it manslaughter.
What if a person whose fantasy was to kill and cook another person met a person who fantasy was to be killed and cooked? Then this happened. What penalty should ensue for the (well-fed) survivor?
And lest you think this is some weird hypothetical, https://en.wikipedia.org/wiki/Armin_Meiwes may enlighten you otherwise.