Seiren is the mysterious alien planet, comprised with mostly a female population. Because the men on Seiren are completely rare and comprise less than 10% of the population (presumably with 90% of the population being female), the women will often go into a crazy frenzy the instant they see one, and attempt to capture the men for themselves in order to mate with them.
Aside from its female inhabitants, Seiren is also home to several dozen unknown, wildlife animal and planet-like creatures.
The planet's location is unknown, however, it is believed to be near Earth, as seen and implied in several episodes.
- Miharu Sena Kanaka
- Maharu Sena Kanaka
- Koyomi Hare Nanaka
- Tomoka Lana Jude
- Nanae Kuh Haruka
- Hijiri Kanata
- Koyomi's Mother
- Seiren is mistranslated as Siren in English printings of the manga.