Mahou Shoujo Artelion ~Aietsu ni Oboreru Kyoudai~

Once, Kamio Kizuna, as the Magical Girl Astraea, repelled the evil association and protected this world. She disappeared, leaving behind her two children - older daughter Chloe and younger son Hikari.

10 years later, the former foes begin their invasion once more. At that time, Magical Girl's powers bloom in Hikari. Chloe, who received instructions about Magical Girl's skills from their mother, supports her younger brother while harboring complicated feelings.

With sister's support, Hikari continues fighting as the Magical Girl Artelion. On one such occasion, Chloe was captured by the enemy. In order to get her back, Hikari follows kidnappers into their world, towards the Hell Castle Nemesis. There, a dangerous trap awaits.

[edited from the official website]