You get this achievement through a dialogue after eating in the nest. It is vital to have the “Alpha Zooloolum” item in your stuff. You can get this from the island called Guyarow. For me there were three that consecutive cut scenes and the final one ended up with them playing strip-a-bobble. The first one was Kay explaining the rules of Alpha zooloolum. Then the next scene was Yu asking to play something else. Then my next cutscene was them playing strip-a-bobble and the achievement popped. If you keep getting the “We should use different ingredients” dialogue, I tried to avoid using appledews and I always used a healing ingredient in the food, because every time I didn’t I got the dialogue. It still took me quite a few sleeping, eating, and going outside rotations but eventually I got it. I hope this helps!