The name Thalassa came from the Greek meaning, "the sea". She is the goddess of the sea. I tried to look up more information about her but there is not much. It is said she take the shape of the sea itself, which was shown in the drama. Furthermore, she was blamed by humankind because of the dangers of the sea. You can read the brief summary of her here (https://www.greeklegendsandmyths.com/thalassa.html).

Back to the drama, we were first introduced to Thalassa (Zoie Tam) when Tsz-Yeuk (Mandy Wong) got transported back to see what the life of an exorcist's wife is like. At that time, the exorcist went to sea to fight Thalassa but never returned. In the end, the wife "went to find him" by jumping into the seas. Fast forward to the present time, Ma Gwai (Kenneth Ma) bumped into Ms. Law (Zoie Tam). She is always drunk when he meets her and is constantly saying she is waiting for someone. They soon developed a friendship.


As we get to know more about her, it is revealed she is Thalassa who took the face of the exorcist's wife back then and has been waiting for him because they never finished their battle back then. Lastly, Ma Gwai turned out to be the reincarnation of the the exorcist she has been waiting for for 700 years. This lead to their final battle in episode 25.

The anticipated battle was lackluster as it showcases nothing from Ma Gwai's side and very little from Thalassa as well. I was expecting a fight but that wasn't the case. When Ma Gwai could've drive into her and 'win' the battle (which would've been lame anyways), flashbacks of them spending time together came up and he just couldn't do it. In the end, she decided to be the one who loses and gave up her powers to him. As she said, she wants him to be the one who remembers her for the next 700 years this time. When you think about it, I think this continues with Ma Gwai's curse. His friends and family will continue to leave him and he will never to be happy. He will always be alone.
In conclusion, Thalassa HAD SO MUCH POTENTIAL to be more than what was given to her. In particular, she has a very powerful ability. Everytime she hums her song, it would compel humans to act on their greatest desires. The tune is so addictive! It's interesting how Ma Gwai was never affected by it though? He was usually with her when she hummed it but acted normal. While others, like Bear Bear, were greatly influenced. I was hoping that this would turn out more exciting so it's a pity she had to disappear in the end.