That Special Drink is an episode of Trapped Within primarily focused on fan service and the development of Kiga's character.
After Kiga ends up having recurring nightmares of himself being killed in combat, he comes to the conclusion that he needs to find a partner in order to prevent the extinction of his race. However, this is no easy task, as the female members of the Union don't like him that well. To assist him with his problem, he calls upon his fellow men in the Union for tips, tricks, and advice, but nothing he does seems to work.
In the end, Kiga finally asks the elusive Chef what his advice is, and much to his surprise, Chef is incredibly eager to help him and is actually very knowledgeable on the topic of love. After explaining the fact that love is based on chemistry, and that Kiga's chemistry is incompatible with humans, Chef makes some "special drinks" that cause his chemistry to become compatible with humans and causes the female Union members to become attracted to him. However, Chef "accidentally" makes the potion for the females incorrectly, which causes the female Union members to become way too forceful with their ways, to the point where they become entranced. Along with this, they end up becoming obsessed with not just Kiga, but with every male Union member, which causes chaos throughout HQ.