Uke is a merman who lives with his father and many much younger siblings at the bottom of Tokyo Bay. Because of pollution and human encroachment, uke and his father must work as humans to provide for the family. This is kinda dangerous because if mermen lie, they turn into bubbles/foam once the sun sets and die. Uke is an office worker who's recently been made a secretary of the rumored demon (not an actual demon, just super scary and mean) president. This was a punishment because uke turned down the daughter of a high status business partner. On arriving at the president's office, he overhears the president shouting about something being late to delivery. The president's fiance, another business partner's daughter, is saying that a huge deal will fall through if this delivery doesn't reach her father on time. The problem is, its impossible to make the delivery by land, but uke thinks he can make it by swimming. Just as he is thinking this, the president opens the door and questions who uke is. Uke explains who he is, but then president asks if he can fix the problem and since uke can't lie, he says that he can make the delivery. The president, our seme, entrust the task to uke, and uke pulls through, but exhausted himself in the process. Upon arriving back to the office, he meets the seme outside and collapses. He wakes up in the seme's office bedroom. Seme questions how uke made the trip and uke has to expose himself to not lie. The rest is just the trope of them coming together because seme is attracted to uke's purity, uke (after remembering that seme has a fiance) thinking that a human would be better off with a human and lying to get away, the seme chasing after uke to save him, them becoming a couple (after seme breaks it off with fiance), and then a bit about their time together after. Happy ending. There are multiple stories after that are all OK oneshots as well. And overall good read.
Junketsu Ningyo