Okay, as much as I love Rocky extending Grace's life without telling him, consider: Rocky *does* tell Grace, Grace just then somehow manages to like. Horrendously misinterpret what the treatment is actually for. Like.
Eridian Doctor: We went through the human genome and found a bunch of places with old broken DNA repair mechanisms so we came up with a gene editing therapy that fixes them in order to extend your lifespan.
Grace: *flashbacks to when Rocky found out that humans can experience long term effects from lower doses of radiation exposure and Grace wasn't being as careful as he should have been back when they first met because he still thought this was gonna be a suicide mission*
Grace (internally): Oh, so cancer prevention! Got it!
Grace: Sounds good!
*like 100 years later*
Grace: Hey Rocky, how am I not dead yet?
Rocky: ???
