You need to get pregnant with a deepone baby which involves doing it with the enemy fishmen that are east of noir or in the fishmen ruins, you also need to avoid getting womb seedbed while trying for a deepone baby if you get seed bed you need to empty self out remove seed bed and try again if you pay attention to your hunger from full you can learn if you were successful or not the next day it will be missing about 5 more hunger than usual. also if you are a moot you also need to do it with a human at least once and also note you should probably have an insane amount of money expect to be pregnant most of the time since its a very long pregnancy compared to the other two i recommend a high wis nympho build with it
(edit:struck through irrelevent wrong information from the post a year ago)