Long Jie is a high school student whose life appears to have been cursed with endless rotten luck. From his family life to his studies and his social life, nothing seems to ever go right for him. When a family tragedy compounds his misery, leaving him alone, he thinks things can't get any worse...until things take a turn for the bizarre.

All of a sudden, he finds himself face-to-face with a merman name Ren Yu. The latter cannot survive out of water for long, and claims that it is Long Rie's fault that he has been brought ashore. Long Jie agrees to help and takes this half-man-, half-sea creature back to his home, where Ren Yu promptly takes over the bathtub! Forced to live with this unlikely marine being, Long Jie eventually finds that Ren Yu is actually quite a lot of fun – although the whole situation gets weirder still when the merman becomes his classmate. But there's magic in the air, and if too long goes by without Ren Yu returning to the sea, there could be trouble ahead. What will become of their friendship when the call of the ocean begins to grow louder?

哇，窗口太小啦

49 Days with a Merman