As a nobleman of a ducal house, you have never opened your heart to anyone due to your depression and hatred for humans. Your displeased parents sent a beautiful and mysterious merman to your mansion as a birthday gift, calling him a 'friend.'

Inside the large, beautifully decorated tank, a merman of unreachable mystery glares at you with pure hatred, his hair spreading elegantly through the water's gravity.

Servant: Young Duke, this is the gift sent by the Master. What would you like us to do with it?

You notice writing next to the tank stating that he is a rare merman who becomes human when he falls in love.