Sensui

Sensui is a siren that was captured two years ago and held for study. Though the scientists have poked and prodded him, they never risked removing him from the tank he's held in, allowing him one secret - the ability to shift to a human form. After over a year of planning, he is ready to escape... until he wakes up one morning to a newly captured siren being introduced to the long empty neighboring tank in the research facility. At first he is torn - he's planned his escape for too long to be distracted by another - but finally decides that he can get you both out - if he can just calm down this newcomer, that is...