Alia (アリア Aria) is Alain and Adel's older sister who once took care of the Fukami siblings. Alia becomes aware of her brother Adel's plans to kill their father Adonis, but before she can act, she crosses paths with Makoto searching for his original body. He thanks her for raising himself and Kanon while they were in the Gamma World and offers to show her the human world, but Alia turns down the offer, knowing that she will be needed in the Gamma World after realizing that Adel has succeeded in assassinating the emperor Adonis, a fact that she relays to Makoto before he leaves. Although Alia finally finds her father alive and imprisoned by Adel, she is warned by her father to stay away from a barrier Adel has imprisoned him in, and tells her to play along with Adel's schemes until Alain returns with a reinforcements. Once Alain returns, backed by his new ally Takeru Tenkūji, Alia reveals to her younger brother that Adel has set up all of the events thus far, including framing him for their father's assassination. When she learns that Adel has finally killed their father, Alia entrusts Takeru to take care of Alain while she remains behind. Once Alia has grown tired of Adel's scheme and ignores Edith's warning not to engage her brother while the Gammisers are with him, she decides to ally with her youngest brother Alain and his allies to stop Adel for his own good by using her own Proto-Mega Ulorder and a pink-colored Necrom Eyecon to transform into Kamen Rider Dark Necrom P (仮面ライダーダークネクロムP（ピンク） Kamen Raidā Dāku Nekuromu Pinku). Her first attempt was to stop Adel from his own madness, but fails due to Gammisers Climate and Planet being too powerful for her and Edith was too late to save her, which leads to her Gamma Eyecon body getting destroyed and returning her to her mortal body where she is currently held captive. Before her father's death, she was told by him his reason to prevent her and her younger siblings from obtaining the Gammisers' power and contacting the Great Eye, is that one of their wishes are too dangerous and may ended being manipulated by Gammisers itself, particularly to prevent Adel due to his stubborn desire allows the Gammisers completely manipulates him for their own plans. After being freed by Alain and their allies, Alia helps Takeru to reveal Adel their father's reason to keep him from nearing the Gammisers, finally redeeming her younger brother. Until the Gammisers completely possessed Adel and before Ghost Mugen Damashii has no choice to kill him along with them, she and Alain keeps Adel's last word from not to ended up like him. When the Gammisers reveal to have a backup plan to store their templates inside Makoto clone's Deep Specter Eyecon and possessed the Great Eye into Great Eyeser, Alia stays in the Gamma world to take care of the mess to clean up, while ensuring her allies successfully stops the Great Eyeser for good.
Alia is portrayed by Reon Kadena (かでな れおん Kadena Reon), who also portrays Alicia. As a child, Alia is portrayed by Emiri (エミリ).