|Name in Japanese||不知火 明乃 明星|
|Rōmaji Translation||Shiranui Akeno Myōjō|
|Voice Actor (Japanese)||Eri Kitamura|
|Voice Actor (English)||Trina Nishimura|
Akeno Shiranui (不知火 明乃 明星, Shiranui Akeno Myōjō) is not only a mermaid but also a "mermaid examiner". She has the responsibility of deporting all the mer-people who fail to qualify as not only resembling humans but also not arousing any suspicion of their true identities.
It is eventually revealed that she is Masa's younger sister which she is unaware of.
When first introduced she had a hostile attitude towards the other major protagonists. This later changes as she develops feelings of compassion towards them and also as she finds her "duty" as a Knight-in-training as an excuse used by the final antagonist. She is terrified of ghosts and has feelings for Nagasumi Michishio.