For this achievement, you’ll have to hatch at least one Monstie with an S Rank Gene. This should be easy enough following the
Conservationist Crown achievement and having multiple S Rank Monsters in your ecosystem.
To do this, you must raise a Monster’s Rank to S by releasing multiple of that monster into the wild from your stables. Once the Monster is S Rank, there’s a chance that eggs will now have an S Rank gene when hatched.
To further increase your chances, it’s best to try and obtain Highly Potent eggs from dens. Eggs from dens come in 3 variants – Fairly Potent (no shine when picked up from the nest), Very Potent (a golden shine when picked up), and Highly Potent, (a white/purple/blue shine and sparkles when picked up).
Once you hatch a Monstie with an S Rank gene, the achievement is yours!