Umi no Uta ga Kikoeru

Senzaki Kaito was born with a small bruise in his throat.
The name of the bruise is “Senjuou”.
His relatives fear the bruise is a sign of a curse.
When Kaito was 17, there was a mysterious murder case known as the Mummy Murder, so named for the victim who looked like a dried up mummy. The townspeople were frightened.
One day he met a beautiful girl named Miu.
She says that she is a mermaid. He doesn’t believe her at first.
Then, Senjuou begins to hurt.
He starts on a journey with his friends to solve the murder and his own mystery.

[Edited from Apple Store and DLsite English]