[ WP ] You tell Death that you will never tire of living no matter how long you live . It makes you a bet that you will and thus grants you true immortality . You 've just lived through the second death of the universe and show no sign of stopping . Death is baffled .

I liked your story but I do have one point to make. 
 
 The story seems not to be written by a truly immortal creature, because I feel that I understand too much of what he's saying. It's still written by someone who is mortal, because things are too clear. Even though you can attribute to the fact that the bath tub analogy is kind of like an ELI5, it does n't feel like an all-knowing creature who tries to explain stuff, since it'll end up being way too complex too if such a creature would exist. 
 
 Nevertheless, great job, your story got me thinking.
