The My Girlfriend is a Mermaid!? is already available on Steam as She is Mermaid—albeit with just Japanese, Simplified Chinese, and Traditional Chinese subtitle support—and the visual novel’s next stop in Japan is Switch.
As for the English version, Sekai Games previously announced plans to bring My Girlfriend is a Mermaid!? to PC and Switch in the west in February, as well, so stay tuned for a concrete date.
Cosen revealed the Switch date during the Digital Games Expo 2018 event in Akihabara.